Leftover Pizza Breakfast Casserole

INGREDIENTS

• cooking spray
• 3 slices leftover pizza, cut into 3/4-inch squares
• 4 eggs, beaten
• 1 cup milk
• 1 (8 ounce) package shredded mozzarella cheese
• 1/3 cup chopped onion
• 3 tablespoons butter, melted
• 1 clove garlic, minced
• 1 teaspoon dried oregano
• 1/2 teaspoon salt
• 1/4 cup grated Parmesan cheese, or to taste
• 1/4 teaspoon red pepper flakes, or to taste