Impossible Cheeseburger Pie - I Ate The 80's

Ingredients

• 1 lb ground beef
• 1 ½ cups chopped onion
• ½ tsp salt
• ¼ tsp pepper
• 1 ½ cups milk
• ¾ cup Bisquick baking mix
• 3 eggs
• 2 tomatoes, sliced
• 1 cup shredded Cheddar or process American cheese