Brown the sausages by placing them in a pan (or seer mode on an InstantPot), and cook them until they turn nice and brown on all sides.
After they've browned, place the browned Italian sausages in your slow cooker.
Add the garlic, peppers, onions, and all the seasonings, then gently pour the marinara sauce over the top.
Put the lid on and cook on LOW for 4–6 hours.
When it’s almost time to eat, toast your hoagie rolls until they’re warm and a little crispy.
To build your sandwiches, put a sausage in the bread, spoon some of the marinara sauce and peppers over the top of the sandwich.
Sprinkle on some shredded mozzarella cheese and let it get a little melty. And Enjoy while the sandwich is hot!