Spray 9-inch pie plate with nonstick cooking spray. Cook ground beef and onion in large skillet over medium heat until beef is browned; drain. Stir in salt and pepper. Spread in pie plate; sprinkle with 1-1/2 cups cheese.
Beat milk, biscuit mix and eggs until smooth. Pour into pie plate over ground beef mixture. Bake in preheated 400°F oven 30 minutes or until golden brown and knife inserted in center comes out clean. Sprinkle with remaining cheese. Let stand 5 minutes before cutting.