Prepare the hot dogs: Using a sharp paring knife, carefully cut a slit lengthwise down the center of each hot dog, ensuring you do not cut all the way through the bottom. The pocket should be wide enough to hold the cheese.

Stuff the hot dogs: Spread a small amount of mustard inside the cavity of each hot dog. Insert one piece of mozzarella cheese stick into each cavity, pushing it down until it is fully encased.

Wrap the beef: Take two slices of the deli roast beef and tightly wrap them around the circumference of each stuffed hot dog, starting from one end and overlapping slightly to ensure the cheese remains sealed inside.

Cook the hot dogs: Preheat grill to medium heat (or oven to 375°F/190°C). If grilling, cook for about 12-15 minutes, turning frequently until the beef is slightly crispy and the cheese has melted. If baking, place on a wire rack over a baking sheet and bake for 18-20 minutes.

Toast the buns and serve: Lightly toast the split rolls on the grill or in the oven. Place the hot beef wraps into the toasted buns. Top immediately with chopped onion and desired condiments.