In a large skillet over medium heat, place the ground beef, onions and garlic. Cook 8-10 minutes until no longer pink; break the beef up into small pieces with a spoon. Drain and discard the fat. Add salt, cornstarch, dried onion, parsley, sugar, garlic powder, green pepper flakes, Italian seasoning, dried oregano, the tomato sauce and the water. Stir over low heat until small bubbles appear around the edges.
Spray a 4qt slow cooker with non-stick spray. Transfer the meat sauce into the slow cooker.
In a bowl, whisk together flour, milk, eggs and mozzarella cheese. Pour carefully over meat sauce. Top with pepperoni and/or olives, if desired. Sprinkle with parmesan, cover, and cook on high 4 hours (3 hrs for a 6qt pot), until the topping is puffed, golden brown, and pulling away from the sides of the pot. (Cooking on low is not recommended.).