2 medium onions, chopped
1/4 cup butter or margarine
2 cans {6-1/2 ounce each} tuna, drained
2 cups shredded Cheddar cheese
1 cup Bisquick. Original Baking Mix
1-1/4 cups milk
1/4 teaspoon salt, if desired
1/8 teaspoon pepper
3 eggs
2 tomatoes, thinly sliced
Serving Size : 6
Heat oven to 400 degrees. Grease square baking dish, 8x8x2 inch. Cook onions and butter in 10-inch skillet over low heat, stirring occasionally, until onions are lightly brown. Sprinkle tuna, 1 cup of the cheese, and the onions in baking dish. Beat Bisquick, milk, salt, pepper, and eggs with wire whisk or hand beater until almost smooth, about 1 minute. Pour over tuna mixture, spreading evenly. Bake until knife inserted in center comes out clean, 25 to 30 minutes. Top with tomato slices and remaining cheese. Bake until cheese is melted, 3 to 5 minutes. Cool 5 minutes.