Preheat the oven to 375°F (190°C).
Cook the lasagna noodles according to package instructions.
Heat olive oil in a large skillet over medium heat.
Add chopped onion and sauté until translucent.
Stir in minced garlic and cook for 1-2 minutes.
Add chopped spinach, zucchini, and red bell pepper, cooking until softened.
Season the vegetable mixture with oregano, salt, and black pepper.
In a separate bowl, mix ricotta cheese with half of the mozzarella and Parmesan.
Spread a thin layer of marinara sauce on the bottom of a baking dish.
Layer cooked noodles, vegetable mixture, cheese mixture, and marinara sauce.
Top with remaining mozzarella and Parmesan cheese.
Cover the dish with foil and bake for 30 minutes.
Remove from oven, let it rest for 10-15 minutes before slicing.