Prep Time: 5
Cook Time: 30
Serves: Serves: 4
Melt butter in large skillet over medium heat. Separate onion slices into rings; add to skillet. Cook uncovered 10 minutes or until golden brown and tender, stirring occasionally.
Form ground meat into four 1/2-inch thick patties. Season with salt and pepper, if desired. Cook in large nonstick skillet or ridged grill pan over medium heat 6 minutes per side or until no longer pink in center.
For each sandwich, lay slice cheese on bread; top with patty, onion, cheese and bread. Coat large skillet with cooking spray. Cook each sandwich over medium-low heat 4 minutes per side or until golden brown and cheese is melted.