Preheat oven to 400°F. Spray two non-stick cookie sheets with cooking spray.
Place sausages on one of the cookie sheets. Bake for 20 minutes.
Using tongs, flip sausages over. Add peppers and onions to the cookie sheet and drizzle with olive oil. Sprinkle peppers and onions with salt and pepper and half of the Italian seasoning. Toss so that all peppers and onions are coated with olive oil and seasoning. Bake 20-25 minutes or until just softened and sausages reach 160°F internally.
Meanwhile, combine butter, remaining Italian seasoning, garlic and pepper in a small bowl.
Open up the hoagie rolls lengthwise, ensuring that they don't fully come apart. Using a basting brush, preferably a silicone one, brush the butter mixture over the inside of each hoagie. Arrange the hoagies on the second baking sheet.
When sausages are finished, switch the oven to the broil setting. Broil the buttered hoagie rolls until just lightly toasted and slightly golden brown, about 1-2 minutes. Don't let them get more toasted than this, or they'll burn at the end of the recipe.
Using tongs, assemble the hoagies with one sausage each and a couple scoops of peppers and onions. Cover each with 1-2 tbsp marinara. You can use more or less sauce depending on your preference. Then arrange the cheese on each hoagie lengthwise so that all of the toppings are covered. Broil until the cheese melts, 1-2 minutes.
Serve and enjoy!