Preheat oven to 450°F. Coat baking sheet with cooking spray. Place sliced zucchini on sheet and sprinkle with pepper. Bake 10 minutes, flip slices and bake another 5 minutes. Remove from oven and reduce oven temp. to 350°F. Brown ground beef over medium heat and drain. Add Italian seasoning and garlic. Simmer. Add onion, peppers and mushrooms. Simmer until veggies are tender. Add tomatoes and tomato paste. Simmer, uncovered, approximately 10 minutes. Set inside. Make ricotta filling by combining ricotta cheese and egg, stir well. To assemble lasagna: Arrange half the zucchini slices over the bottom of a baking dish, sprinkle with 2 tbsp Parmesan cheese and top with half the meat filling. Dot the ricotta cheese filling over the meat filling. Layer the remaining zucchini, Parmesan and meat filling. Bake uncovered for 20 minutes. Sprinkle mozzarella cheese over top and bake an additional 10 minutes or until cheese is melted. Remove from oven and let stand 20 minutes before serving.