Cook The Vegetable Lasagna Filling: Quarter all 4 zucchini and thinly slice. Dice all 3 bell peppers and mince 3 cloves of garlic. Heat olive oil in a large skillet over medium high heat.
Make The Marinara Sauce: Mince 3 cloves garlic. Spray a medium sized saucepan with cooking spray and lightly saute the garlic and remaining red onion until the onion is translucent.
Mix The Cheese: Combine 1.5 cups of the ricotta cheese and 1 cup of the mozzarella in a bowl. Keep the Parmesan cheese (or Italian blend, if using) separate.
Assemble The Vegetarian Lasagne: Spray the bottom of a large casserole dish or baking dish with cooking spray. Put 1 cup sauce at the bottom of the dish.