Slow Cooker Cheese Steaks

2 pounds beef tri tip steak

1 cup beef stock

1 tablespoon red wine vinegar

1 tablespoon Worcestershire sauce

2 teaspoons olive oil

1 large onion, sliced

1 large green pepper, sliced

8 ounces sliced fresh mushrooms

12 slices white American cheese

6 French or Italian sandwich rolls, split

Place beef in the slow cooker crock. Pour beef stock, vinegar, and Worcestershire over beef. Cook on Low until beef is cooked to medium, 3-4 hours. Remove cooked beef from broth and set aside. Reserve broth.

Preheat an oven to 350 degrees F (175 degrees C).

Heat oil in a large skillet over medium-high heat. Cook mushrooms in oil until they begin to soften; add onion and green pepper. Cook and stir until vegetables are soft, about 5 minutes.

Slice beef thinly. Divide beef and vegetables evenly among the rolls. Top each sandwich with 2 slices cheese; wrap in foil.

Place sandwiches in preheated oven and heat until cheese is melted; about 10 minutes. Serve hot sandwiches with reserved beef broth, if desired.