Brown beef with onion in large skillet; drain. Add sauce mix, tomato sauce, water, and oregano. Simmer 10 minutes. Spoon into greased 9x13 baking dish. Top with mozzarella cheese. Keep hot in 400 oven while preparing batter.

Prepare batter by beating together the eggs, milk, and oil. Add flour and salt and beat until smooth. Pour over hot pizza filling. Sprinkle with Parmesan cheese.

Bake at 400 for 30 minutes or until puffed and dark brown.