Preheat oven to 325 degrees.
Brown the ground beef or ground turkey in a large pot over medium heat, stirring frequently.
Add in garlic, onion and green pepper, and continue to sauté for 5 minutes.
Stir in marinara sauce.
Bring sauce to a light boil, then remove from heat.
Add 1/4 c. Parmesan cheese and stir. Set the rest aside.
Place a thin layer of the sauce in a 9x13 baking dish.
Layer zucchini and mushrooms over sauce, then mozzarella cheese.
Repeat, alternating layering of sauce, then zucchini and mushrooms.
Finish with layer of mozzarella cheese on top and sprinkle with remaining Parmesan cheese.
Bake lasagna at 325°F for 15 minutes, covered with foil.
After 15 minutes, remove foil, increase temperature to 350°F, and bake for an additional 15 minutes.