Heat oven to 400 degrees F. Grease a 9-inch pie plate.
Cook beef and onion in skillet until brown, 6 to 8 minutes. Carefully drain off any fat. Stir in salt.
Spread beef mixture in prepared pie plate. Sprinkle with cheese.
Whisk together baking mix, milk and eggs in a medium-size bowl until completely blended. Pour over beef mixture in pie plate.
Bake in 400 degree F oven 25 minutes or until knife inserted in center comes out clean. Let cool slightly, about 5 minutes. Cut into wedges. Makes 6 servings.