6 chicken breast
Sliced Provolone or Swiss Cheese (use the cheese you like the best- I prefer Provolone in this sandwich)
Place chicken in a slow cooker and sprinkle onion soup mix and black pepper over the top. Add onions and stock. Cook on low 7-8 hours. Remove chicken and shred and return to slow cooker for an additional 30 minutes.
While chicken is finishing cooking, cut the buns in half and place a piece of cheese on each half. Broil the buns to toast the bread and melt the cheese. This will only take a minute or two, and make sure to keep a careful eye to prevent burning.
On the bottom bun, spoon chicken on top of the cheese and cover with remaining bun half. Serve immediately.