Impossible Cheeseburger Pie
["1 lb. ground beef", "1 1/2 c. chopped onion", "1 1/2 c. milk", "1 tsp. salt", "1/4 tsp. pepper", "2 tomatoes, sliced", "3/4 c. Bisquick baking mix", "2 c. Cheddar cheese", "3 eggs"]
["Heat oven to 400\u00b0.", "Grease a 10-inch pie plate and set aside."]
["ground beef", "onion", "milk", "salt", "pepper", "tomatoes", "Bisquick baking mix", "Cheddar cheese", "eggs"]