Ingredients

• 2 tablespoons olive oil
• 1 ½ cups chopped yellow onion
• 1 red bell pepper, chopped
• 8 ounces cremini mushrooms, chopped
• 2 medium zucchini, chopped into ½-inch pieces
• 4 cloves garlic, minced
• 48 ounces marinara sauce
• 1 teaspoon dried Italian seasoning
• Salt and pepper, to taste
• 2 pinches crushed red pepper flakes, or to taste
• ¼ cup chopped fresh parsley
• 5 ounces baby spinach, coarsely chopped
• 1 egg
• 1 cup ricotta cheese (8 ounces)
• 9 oven-ready (no-boil) lasagna noodles
• 16 ounces shredded mozzarella cheese (about 4 cups)
• ½ cup grated Parmesan cheese
• Chopped fresh basil or parsley, optional, for serving

Instructions

1. Preheat the oven to 375°F.
2. Heat the olive oil in a large skillet or Dutch oven over medium-high heat. Add the onion, bell pepper, mushrooms, and zucchini. Cook for 7 to 8 minutes, stirring occasionally, until the vegetables have softened. Stir in the minced garlic and cook for 30 seconds.
3. Add the marinara sauce, Italian seasoning, salt, pepper, crushed red pepper flakes, and parsley. Stir well, bring the mixture to a gentle simmer, then reduce the heat to low. Let it cook for 10 to 15 minutes, stirring occasionally. Stir in the chopped spinach until combined.
4. While the sauce cooks, lightly beat the egg in a medium bowl with a fork. Add the ricotta cheese and mix until smooth. If needed, shred the mozzarella cheese during this time.
5. Spread about 1 cup of the vegetable sauce across the bottom of a 9×13-inch baking dish. Arrange 3 lasagna noodles over the sauce. Spoon ⅓ of the remaining sauce over the noodles. Dollop half of the ricotta mixture across the sauce, then sprinkle with ⅓ of the mozzarella and ⅓ of the Parmesan.
6. Repeat the layers one more time using 3 noodles, half of the remaining sauce, the remaining ricotta mixture, half of the remaining mozzarella, and half of the remaining Parmesan.
7. Finish with the final layer by adding the remaining 3 noodles, the rest of the sauce, and topping everything with the remaining mozzarella and Parmesan.
8. Spray one side of a sheet of aluminum foil with cooking spray and cover the baking dish with the sprayed side facing the cheese to prevent sticking.
9. Bake on the center oven rack for 35 minutes while covered. Place a rimmed baking sheet on the rack below to catch any sauce that may bubble over.
10. Remove the foil and continue baking for 10 to 15 minutes, or until the cheese is lightly browned and the sauce is bubbling around the edges.
11. Allow the lasagna to rest for 15 minutes before slicing and serving. This resting period helps the layers hold together for cleaner slices.

Notes

Make Ahead

Assemble the lasagna up to 24 hours in advance, then cover and refrigerate. If baking straight from the refrigerator, increase the covered baking time by approximately 15 minutes.

Freezing Before Baking

Wrap the unbaked lasagna tightly and freeze for up to 3 months. Thaw in the refrigerator for 24 hours before baking. Since it will be cold, allow an additional 15 minutes during the covered baking stage.

Storing Leftovers

Store leftover baked lasagna in an airtight container in the refrigerator for 3 to 4 days, or freeze for up to 3 months. Individual portions freeze especially well for quick meals. Thaw overnight in the refrigerator whenever possible, then reheat in the microwave or in a covered baking dish until thoroughly heated.

Smaller Batch

For a smaller serving size, prepare half the recipe and bake it in a 9×9-inch baking dish.