Cut peppers in half from stem to bottom.pull out seeds and stem. Spray a baking dish with non stick spray and place peppers in dish. Place a slice of cheese in the bottom of each pepper

Slice the onion while the oil is heating in a large skillet over medium heat. Once oil is hot ,put the onion in the pan and Sautee until onions are caramelized, about 10-15 min.

Cut the roast beef into chunks. Put the meat in the pan with the onions. Add the beef broth to the pan and bring to a boil. Add salt and pepper.

Once most of the liquid has evaporated. Spoon the mixture into the peppers. Bake at 375°F for 25 min. Until the peppers are soft.

Take the peppers out and spread some mayo on top. Top them off with a slice of cheese. Put back in the oven until melted.