Preheat the broiler to high. In a skillet, add in the olive oil and butter. Melt and then stir in the garlic and Italian seasoning. Remove from heat and brush this mixture generously over the hoagie buns - inside and out. Place the hoagie buns on a sheet pan and broil for 1-2 minutes on high until very lightly golden brown (you'll add them back later).
Begin the sausages cooking. Remove the casing and follow package directions to grill the sausages. If you don't have the sausage grill, remove casings, slice the sausages into 1-inch thick pieces and add to a skillet (same one you used earlier for the butter) over medium heat. Cook for about 2 minutes stirring occasionally and then add in the onion and garlic. Cook for another minute.
Add in the bell peppers, marinara sauce, Italian seasoning, and pepper. Bring the mixture to a boil and then simmer for 5-6 minutes or until the peppers are crisp tender.
Separate the mixture evenly among the hoagie buns and sprinkle generously with cheese.
Return the hoagies to the oven and broil for another 1-2 minutes or until cheese is melty.
Top with fresh basil or parsley if desired and enjoy immediately.