Preheat the oven to 550 degrees F.
Form the sausage into an 8-inch-long patty. Then place in a small ovenproof pan or skillet and roast until almost cooked through and the bottom of the patty begins to brown, about 10 minutes. Transfer the pan to the stovetop, and set over medium-high heat. Flip the patty using a large spatula. Add the onions to the pan to cook in the rendered fat. When the onions soften and just begin to brown, place the sausage and onions in the hero roll. Top with the tomato slices and shredded mozzarella. Place the sandwich in the oven to toast and completely melt the mozzarella, 4 to 5 minutes. Cut the hero in half, and serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Lee's Tavern, Staten Island, NY