Steak Sandwich with Peppers

1 tablespoon olive oil
1 medium onion, halved and sliced into 1/4-inch-thick wedges
1 red bell pepper, thinly sliced
1 green bell pepper, thinly sliced
Coarse salt and ground pepper
2 tablespoons red wine vinegar
Reserved Chili-Rubbed Skirt Steak, very thinly sliced
4 hero rolls, split in half horizontally, insides torn out to form a hollow
6 ounces thinly sliced (about 10 slices) pepper jack cheese

Preheat broiler with rack 6 inches from heat. In a large skillet, heat oil over medium-high. Add onion and peppers; cook, stirring often, until softened and beginning to char, 10 minutes. Season with salt and pepper. Remove from heat; stir in vinegar and steak.

Place bottom halves of rolls on a large rimmed baking sheet; dividing evenly, top each with meat mixture, then cheese slices. Broil until cheese has melted, about 2 minutes. Remove from oven; transfer to a cutting board.

Source: Martha Stewart