In a large skillet, cook the sausages in a drizzle of oil, covering if needed, until cooked through.
Transfer to a plate and add a thinly sliced onion and seeded red bell pepper to the pan along with another drizzle of oil.
Cook, stirring to loosen any browned bits on the bottom of the pan, until the veggies are soft and golden.
Stuff split hoagie or hot dog buns with the sausages, top with the peppers and onions and scatter some grated mozzarella, Gouda or Monterey Jack cheese on top.
Place on a baking sheet and run under the broiler for a minute or two, until the cheese melts.