Caramelized Onion, Mushroom and Spinach Lasagna

Recipes By Cara
October 7, 2018

Caramelized Onion, Mushroom, & Spinach Lasagna is delicious, light and easy to make! It is the perfect light and healthy meal for lunch or dinner, and great for vegetarians.  Serve with a Classic Italian salad.

Each layer in the Caramelized Onion, Mushroom, & Spinach Lasagna is a star in this dish.  The caramelized onions are deglazed with balsamic vinegar and pair perfectly with the creamy ricotta cheese.  The sautéed mushrooms and wilted spinach are nestled with shredded mozzarella cheese for the second layer.  The top layer is more sauce and freshly grated Parmesan cheese.  Assemble the lasagna with no-boil lasagna pasta sheets and store-bought marinara sauce to speed up the process. Cook the fresh vegetables in the same skillet to minimize cleanup.  I made the lasagna pictured here with a spicy Arraribiata Sauce instead of classic Marinara. We just like the the extra flavor.  That is up to you.

Here is the step-by-step guide:

Gather your ingredients and prepare each layer.  First sautee mushrooms in olive oil and butter with a little thyme.  Transfer to a plate and Set aside to cool.

sautéed mushrooms

Sautee fresh, chopped spinach in olive oil with a some grated nutmeg, salt and pepper until just wilted.  Transfer to a plate and set aside to cool.

sauteed spinach

Make the caramelized onions. Sautee raw, sliced sweet onions in the same skillet with lots of butter and olive oil.

raw onions in skillet

Cook for about 20 minutes over medium heat until golden brown and slightly crisped on the edges.

Deglaze the pan with balsamic vinegar, and cook for 2 more minutes until thick and luscious.

caramelized onions

Prepare the ricotta cheese filling. Mix ricotta cheese, an egg, Parmesan and Romano cheese until well combined.  Season with black pepper and nutmeg.

ricotta cheese

Assemble the lasagna in a 10 x 14 inch lasagna pan.  To make the first layer, place some Marinara sauce on the bottom of the pan. Add a layer of no-boil noodles. Top with the Ricotta cheese filling.  Place the Caramelized Onions on top of the ricotta filling.

First layer

Make the second layer of the lasagna. Add a layer of no-boil noodles on top of the onions. Cover the noodles with more Marinara sauce. Spread the sautéed mushrooms over the sauce. Sprinkle shredded mozzarella cheese over the mushrooms.  Place the wilted spinach over the mozzarella cheese.

Second layer

Finish with the top layer. Add a layer of no-boil pasta noodles. Cover with more Marinara sauce. Generously sprinkle the remaining Parmesan Cheese on top.

Top layer

Cover with foil and bake at 375 degrees for 45 -55 minutes. Remove the cover during the last 10 minutes to brown the top.

baked lasagna

Allow to cool for about 10 minutes and cut in slices with a sharp knife.  Serve with extra Marinara and grated cheese on the side.


Cheese Filling

  • 32 ounces ricotta cheese
  • 1 egg
  • 1 cup freshly grated parmesan cheese
  • ½ cup freshly grated romano
  • 1 teaspoon freshly grated nutmeg
  • 1 teaspoon ground black pepper

Caramelized Onions layer

  • 2 tablespoons butter
  • 2 tablespoons olive oil
  • 2 large sweet onions sliced
  • ½ teaspoon salt
  • ½ teaspoon black pepper
  • 1-2 tablespoons balsamic vinegar
  • Pinch red pepper flakes optional

Mushroom layer

  • 1 tablespoon butter
  • 1 tablespoon olive oil
  • 1 sprig thyme leaves stripped of stem
  • ½ teaspoon salt
  • ½ teaspoon black pepper

Spinach Layer

  • 12 ounces fresh spinach washed and roughly chopped
  • 1 tablespoon olive oil
  • 1/8 teaspoon freshly grated nutmeg
  • ½ teaspoon Kosher salt
  • ½ teaspoon ground black pepper

Final Assembly

  • 12 - 16 ounces no-boil lasagna sheets enough to fit 3 layers in a 10 x 14 pan
  • 10 ounces mozzarella cheese shredded
  • 24 ounces good quality fresh Marinara (or Arrabbiata sauce), store bought or homemade
  • ¼ cup parmesan cheese for top


  1. Preheat oven to 375 degrees. Spray a 10x14 inch casserole dish with cooking spray or grease with olive oil.

To make the ricotta filling

  1. In a medium bowl, mix ricotta cheese, parmesan and romano cheeses, nutmeg, and pepper together until well combined. Set aside

To make the Caramelized Onions

  1. Heat butter and olive oil on high heat in a large skillet. Add the sliced onions and cook on high heat for about 10 minutes, constantly stirring with spatula. Reduce heat to medium and continue cooking for 10 more minutes. Keep stirring to prevent burning on the bottom. Cook for 10 more minutes or until the onions are a deep golden brown. Add the balsamic vinegar to deglaze the pan. Transfer the mixture to a plate to cool.

Prepare the Spinach

  1. Add 1 tablespoon olive oil to large skillet over medium high heat. Add freshly washed and chopped spinach, nutmeg, salt and pepper and toss. Cook for 5 -7 minutes or until just wilted. Set aside to cool.

Prepare Mushrooms

  1. Heat olive oil on high heat in a large skillet. Add the sliced mushrooms, salt, thyme, black pepper (and red pepper flakes if using) and mix. Cook on medium high heat for about 10 minutes, stirring occasionally to prevent sticking, until golden brown. Transfer to a plate to cool.

To assemble the casserole

  1. Make first layer: Place ½ cup marinara on bottom of prepared 10 x 14 baking pan. Add one layer of lasagna sheets. Spread all of ricotta mixture over the lasagna sheets. Spread all of the carmelized onions on top of the ricotta layer.

    Make second layer: Add half a layer of noodles on top of the onions. Add ¾ cup marinara sauce over noodles. Place mushrooms evenly over the sauce. Sprinkle with handfuls of mozzarella cheese. Place cooked spinach evenly on top of mozzarella cheese. Sprinkle rest of mozzarella over spinach.

    Make top layer: Add layer of noodles on top of second layer. Spread rest of marinara sauce evenly over the top of the noodles. Sprinkle the top with parmesan cheese.

  2. Cover the pan with foil. Bake at 375 degrees for 45 - 55 minutes or until the top is golden brown and the sides are bubbling. If needed, remove the foil from the pan the last 10 minutes to brown the top.

  3. Remove from oven and allow to cool for 10 minutes.

    Cut in squares and serve immediately with extra Marinara on the side.

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Cara Kretz

Are you a busy foodie looking for fabulous recipes and menu ideas? This is the place for you. Learn Cara's tips and tricks to being a great home cook. Food, family and love are everything.

For more delicious recipes visit her food blog.