Add ground beef and onion to a large skillet and cook until beef is browned and onion is softened. Drain grease. Spread mixture in a 9-inch grease pie pan.
Sprinkle cheese over meat.
Add milk, onion soup mix, Bisquick and eggs to a medium bowl and whisk together to combine. Pour mixture in pie plate.
Bake for 25 minutes. Let cool a few minutes before serving.