Preheat oven to 425°; roughly chop onion/pepper mix into bite-size pieces + thinly slice sirloin against grain; in a bowl, mix beef, onion/peppers + 6 tbsp sauce; set aside

Place 2 large pieces of foil on a sheet pan + oil the foil; divide mix into the center of each piece of foil + top each with 1-2 slices cheese

Bring the long edges of foil together + roll to seal, leaving 1-inch of space above ingredients; repeat with side ends of foil—your pack is sealed!

Bake 25-27 min then divide to plates