- 2 tablespoons olive oil
- 12 ounces fresh cremini mushrooms, quartered lengthwise
- 1 cup chopped onion (from 1 [11-oz.] onion)
- 1 (24-oz.) jar marinara sauce
- 6 ounces pepperoni slices, divided
- Cooking spray
- 8 (1 3/4-oz.) frozen garlic bread slices, thawed
- 8 ounces mozzarella cheese, shredded (about 2 cups)
- 1 ounce Parmesan cheese, grated (about 1/4 cup)
- ½ teaspoon crushed red pepper (optional)
- Step 1 Preheat oven to 425°F with rack in bottom position. Heat oil in a large skillet over high. Add mushrooms and onion; cook, stirring often, until mushrooms are browned and softened, 7 to 8 minutes. Stir in marinara sauce and 4 ounces of the pepperoni (about 56 slices). Remove from heat.
- Step 2 Coat a deep 13- x 9-inch casserole dish with cooking spray. Arrange garlic bread, lying flat with cut sides up, in casserole dish. Top evenly with mushroom-pepperoni mixture. Sprinkle with mozzarella. Arrange remaining 2 ounces pepperoni (about 28 slices) over mozzarella. Sprinkle with Parmesan. Bake in preheated oven until cheese is bubbly and lightly browned, 12 to 15 minutes. Let stand 5 minutes. If desired, sprinkle with crushed red pepper.