Preheat your oven to 375°F (190°C) and grease a standard muffin tin with cooking spray or olive oil.
In a large mixing bowl, combine the flour, baking powder, salt, garlic powder, and Italian seasoning. Mix well.
Stir in the mozzarella and Parmesan cheeses until evenly distributed.
In a separate bowl, whisk together the milk, olive oil, and egg until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Gently fold in the marinara sauce, cooked sausage, pepperoni, and any optional ingredients like bell peppers or olives.
Spoon the batter into the prepared muffin tin, filling each cup about 3/4 full.
Bake for 20-25 minutes, or until the muffins are golden brown and a toothpick inserted into the center comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.
