Spray crock pot with non-stick cooking spray or use a slow cooker liner. Cut meat into thin strips, place in slow cooker.
Add green pepper, onion, stock, garlic salt, pepper and dressing mix. Cover and cook on low 7 to 8 hours, or high for 3 to 4 hours.
Spoon meat mixture onto toasted buns, top with cheese. You can then put the sandwiches on a baking sheet and bake an additional few minutes to melt the cheese and toast the sandwich. You can also serve with sliced sautéed mushrooms on top.
