Turn oven control to broil. Spray broiler pan with cooking spray.
On broiler pan, arrange zucchini in single layer. Lightly spray with cooking spray; sprinkle with 1/4 teaspoon of the salt and 1/8 teaspoon of the pepper. Broil 15 minutes, turning once, until tender. Remove zucchini to paper towel-lined plate to drain. Pat zucchini dry with paper towels; set aside.
On same broiler pan, arrange mushrooms, cap sides up. Lightly spray with cooking spray; sprinkle with remaining 1/4 teaspoon salt and 1/8 teaspoon pepper. Broil 15 minutes, turning occasionally, until tender. Remove mushrooms to paper towel-lined plate to drain. Pat mushrooms dry with paper towels; set aside.
Heat oven to 375°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In medium bowl, stir ricotta cheese, eggs and 1/4 cup of the Parmesan cheese.
Spread 3/4 cup of the marinara sauce in bottom of baking dish. Layer zucchini slices, overlapping, over sauce. Spread 1/2 of ricotta mixture over zucchini; sprinkle with 3/4 cup of the mozzarella cheese. Top with 3/4 cup marinara sauce. Layer roasted bell peppers, overlapping, over sauce. Spread remaining ricotta mixture over peppers; sprinkle with 3/4 cup mozzarella cheese. Top with 3/4 cup marinara sauce. Arrange mushrooms, cap sides up, over sauce. Spread remaining marinara sauce over mushrooms; sprinkle with remaining 1/2 cup mozzarella cheese and 1/4 cup Parmesan cheese.
Bake uncovered 30 minutes or until cheese is melted and sauce is bubbly. Let stand 10 minutes before serving.