1 tablespoon olive oil
4 Italian-frying peppers, cut into 1/2-inch pieces
1 medium yellow onion, sliced (about 1 cup)
1 medium red onion, sliced (about 1 cup)
1/3 cup beef broth
1 teaspoon balsamic vinegar or red-wine vinegar
1/2 teaspoon salt
1/4 teaspoon black pepper
12 ounces lean roast beef, cut into 1/2-inch strips
4 small whole wheat grinder rolls
1 cup shredded light cheddar cheese

Directions
In a large nonstick skillet, heat oil over medium heat. Add peppers, yellow onion, red onion, and broth. Sauté until peppers and onions are soft, about 10 minutes. Stir in vinegar, salt, and pepper.

Stir roast beef into skillet. Divide mixture over bottom of rolls. Sprinkle with cheese.

Preheat the broiler. Line broiler pan with foil and spray with cooking spray. Place sandwiches on prepared broiler pan. Broil 6 inches from heat, just until cheese melts. Transfer sandwiches to serving plates. Replace roll tops. Serve immediately.

Serves 4