Heat oven to 400 degrees F. Spray a 9-inch glass pie plate with cooking spray.
In a 10-inch skillet, cook beef and onion over medium heat for 8 to 10 minutes, stirring occasionally until beef is brown. Drain and stir in salt.
Spread beef mixture in the pie plate. Sprinkle with Cheddar cheese.
In small bowl, stir Bisquick mix, milk, and eggs with a fork or wire whisk until blended. Pour into pie plate.
Bake about 30 to 35 minutes or until knife inserted in center comes out clean.