Pizza Frittata

Ingredients: 8 large eggs 1/2 cup milk (or a milk alternative) 1 cup shredded mozzarella cheese 1/2 cup grated Parmesan cheese 1 cup marinara sauce 1/2 cup sliced pepperoni or cooked sausage (optional) 1/2 cup diced bell peppers 1/4 cup diced onions 1/2 cup sliced mushrooms 1/4 cup sliced black olives