Brown beef with onion in large skillet, stirring to crumble; pour off excess fat. Add contents of sauce mix envelope, tomato sauce, and water; simmer 10 minutes. Spoon into greased 13 x 9" baking pan. Top with mozzarella cheese. Place in 400 degree oven to keep hot.
To prepare batter, beat together eggs, milk and oil with rotary beater. Add flour and salt. Beat until smooth. Pour over hot pizza filling, being careful to cover filling completely. Sprinkle with Parmesan cheese. Bake at 400 for 30 minutes, until puffed and deep golden brown. Cut into squares and serve at once. Makes 6 to 8 servings