Grease a 6 quart crockpot with cooking spray then pour half the marinara sauce into the bottom. Set aside.
Heat a large skillet over medium high heat.
Once hot, grease with cooking spray then add in sausage links and cook until both sides are nicely seared (if your skillet is small, you may need to do this in 2 batches).
Place seared sausages into crockpot.
Top with peppers, onions, basil, Italian seasoning, oregano, garlic powder, salt and remaining marinara.
Cover and cook on low for 6-8 hours or high for 3-4 hours.
Stir to combine and taste and re-season, if necessary (I sprinkled on more salt).
Optional, but highly recommended - remove cooked sausages, slice into coins, then stir back into the crockpot.
Preheat broiler, then assemble the sandwiches: slice the hoagie roll in half, place both halves onto a baking sheet, top the bottom half with desired amount of sausage/pepper mixture, then two slices of cheese.
Broil until cheese is melted and the top bun is toasted.