Step 1

Preheat oven to 350°F. Spray a 9 x 13 baking dish with cooking spray or oil mister.

Step 2

Heat olive oil in a large skillet over medium heat. Add onion and cook until softened, about 4 minutes. Add zucchini and mushrooms and cook until softened and liquid has boiled off, about 7 minutes more. Remove from heat.

Step 3

Add pasta, marinara sauce, ricotta, salt, and pepper to skillet with vegetables. Stir until well combined.

Step 4

Pour pasta mixture into baking dish. Top with cheese. Bake for 30 minutes. Sprinkle with parsley before serving, if desired.