Rich and gooey, this deep-dish pizza-flavor casserole puffs up as it bakes. It's as much fun to make as it is to eat -- a surefire bet for kids.
Preheat oven to 400°F. In an extra-large skillet, cook ground beef over medium heat until brown; drain off fat. Stir onion, sweet pepper, garlic, dry spaghetti sauce mix, and oregano into meat. Add tomato sauce and the water. Cook and stir until boiling; reduce heat. Cover and simmer for 10 minutes.
Meanwhile, in a medium mixing bowl, beat milk, eggs, and oil with an electric mixer on medium speed for 1 minute. Add flour and salt; beat for 2 minutes more.
Transfer hot beef mixture to an ungreased 3-quart rectangular baking dish. Sprinkle with mozzarella cheese. Pour egg mixture evenly over top. Sprinkle with Parmesan cheese; top with pepperoni slices (if desired).
Bake, uncovered, for 25 to 30 minutes or until puffed and golden. Serve immediately.