1. 1. Prep your veggies: dice onion, mince garlic, dice bell peppers and zucchini, slice mushrooms, and chop spinach.

2. 2. Sauté aromatics: Heat olive oil in a large skillet or Dutch oven over medium heat. Add diced onion and cook until soft and translucent, about 5-7 minutes. Stir in minced garlic and cook for 1 minute until fragrant.

3. 3. Cook hearty vegetables: Add diced bell peppers, zucchini, and sliced mushrooms. Season with salt and black pepper. Sauté for 8-10 minutes, stirring occasionally, until softened.

4. 4. Wilt spinach: Stir in chopped spinach and cook for 2-3 minutes until wilted. Remove skillet from heat.

5. 5. Prepare ricotta mixture: In a medium bowl, combine ricotta cheese, 1/2 cup Parmesan cheese, egg, parsley, oregano, and optional red pepper flakes. Stir well.

6. 6. Preheat oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish.

7. 7. Start layering: Spread 1 cup marinara sauce over bottom of dish. Arrange a single layer of no-boil lasagna noodles over sauce (break to fit). Spread half of ricotta mixture over noodles. Spoon half of sautéed vegetables over ricotta. Sprinkle 1 cup mozzarella cheese over vegetables. Drizzle 1 cup marinara sauce over mozzarella. Repeat layers (noodles, ricotta, vegetables, mozzarella, sauce) once more.

8. 8. Final layer: Place final layer of noodles on top. Pour remaining marinara sauce over noodles, spreading to edges. Sprinkle with remaining 1 cup mozzarella and extra Parmesan.

9. 9. Bake: Cover tightly with aluminum foil. Bake for 30 minutes. Remove foil and bake for another 15-20 minutes until cheese is bubbly and golden brown.

10. 10. Rest: Let lasagna rest for 15-20 minutes before slicing and serving.