Prep Time: 10
Cook Time: 10
Serves: Serves: 2
Melt butter in a large nonstick skillet over medium heat. Add onion rings; cook, stirring frequently, until tender and golden brown, about 5 minutes. Transfer to small bowl; add peppers and toss.
Add sliced steak to same skillet. Sprinkle garlic salt and pepper over steak; stir-fry just until meat is barely pink in center, 3 to 4 minutes.
Pile steak into rolls; top with onion mixture and cheese.