Ingredients:

  Amount  Measure       Ingredient -- Preparation Method
--------  ------------  --------------------------------
   2      cups          onions -- chopped
     1/4  cup           butter
   2      cans          tuna -- 6/2 oz -drained
   2      cups          cheddar -- shredded
   3                    eggs
   1 1/4  cups          milk
   1      cup           Bisquick
     1/4  teaspoon      - salt
     1/8  teaspoon      - pepper
   2                    tomatoes -- thinly sliced

Preparation:

Preheat oven to 400F Grease pie plate 10x1 1/2". Cook onions and butter in 10" skillet over low heat, stirring occasionally, until onions are a light brown. Sprinkle tuna, 1 cup of cheese and onions in plate. Beat eggs, milk, Bisquick, salt and pepper until smooth 15 seconds in blender on High or 1 minute with hand beater. Pour into plate. Bake until knife inserted in center comes out clean, 25 to 30 minutes. top with tomato slices and remaining cheese is melted 3 to 5 minutes. Cool 5 minutes. Source: "The Best of Bisquick"