Preheat oven to 350 degrees F. Coat a 9×13 baking dish with cooking spray and set aside. Bring a large saucepan of water to a boil. Cook spaghetti 3 minutes short of package instructions and drain.
In a large skillet, cook the ground beef over medium-high heat until meat is no longer pink. Add the onions, peppers, mushrooms, zucchini, garlic, salt and pepper to the skillet. Cook, stirring, for 3 to 5 minutes, or until vegetables begin to soften. Add spaghetti sauce and cook for an additional 3 minutes.
Layer the baking dish as follows: half of the spaghetti noodles, half of the sauce mixture, ricotta cheese, oregano, the remaining spaghetti noodles, the remaining sauce, cheddar cheese, Parmesan cheese and parsley. Bake uncovered in the preheated oven for 30 minutes. Serve warm with a crusty bread and salad.