Start with the sliced onions in the bottom of the slow cooker. Then layer on red and green bell peppers.
Sprinkle veggies with garlic powder, Italian seasonings, and red pepper flakes. Then evenly pour crushed tomatoes over the top.
Next, layer in the sausages in a single layer. Secure lid on a slow cooker and cook for 6 hours on low. Every hour or so, give the slow cooker a little jiggle to help the sausages sink down into the sauce some.
Split your crusty rolls and place two slices of mozzarella in the fold. Then add a piece of sausage and a portion of peppers and onions. You might want to slice it in half when you serve it.
Keyword bell peppers, Italian Sausage, red sauce, sandwich, Sausage, slow cooker