Impossibly Easy Cheesburger Pie

1	lb lean (at least 80%) ground beef
1	medium onion, chopped
1/2	teaspoon salt
1/8	teaspoon pepper
1	cup shredded Cheddar cheese (4 oz)
1/2	cup Bisquick® Gluten Free mix
1	cup milk
3	eggs Heat oven to 400°F. Spray 9-inch glass pie plate with cooking spray. In 10-inch skillet, cook beef and onion over medium-high heat, stirring frequently, until beef is thoroughly cooked; drain. Stir in salt and pepper. Spread in pie plate; sprinkle with cheese. In medium bowl, stir Bisquick mix, milk and eggs until blended. Pour into pie plate. Bake 25 to 30 minutes or until knife inserted in center comes out clean.