Preheat oven to 375°F (190°C) and grease a 9x13-inch baking dish.
Cook lasagna noodles according to package instructions, then drain and set aside.
In a skillet, sauté diced onions, bell peppers, zucchini, and mushrooms until tender.
Stir in crushed tomatoes, tomato sauce, garlic, basil, oregano, salt, and pepper to taste.
In a separate bowl, mix ricotta cheese, shredded mozzarella, and grated Parmesan.
Spread a layer of the vegetable-tomato sauce mixture on the bottom of the baking dish.
Layer cooked lasagna noodles, followed by the cheese mixture, and repeat until all ingredients are used.
Cover with foil and bake for 30 minutes, then uncover and bake for an additional 15 minutes until bubbly and golden. Enjoy your delicious veggie lasagna!