Add in the bread crumbs, milk, parmesan, salt, pepper, and garlic powder. Mix those together.
Add in the beef and Italian sausage, breaking them up with your hands.
With your hand, mix these all together and then form meatballs that are about the size of a ping pong ball. Place the meatballs on a large baking sheet that is lined with parchment paper.
Bake these for 8 minutes. Remove the pan from the oven and set aside for now.
Meanwhile, heat the oil in your electric skillet. Add in the onion, pepper, and garlic. Sauté these until tender. Add in the remaining ingredients and whisk them together. Bring the mixture to a boil and then reduce the heat to very low.
Gently nestle your meatballs down into the sauce. Let them simmer on very low heat for 1-2 hours.
To serve the sandwiches, layer some sliced cheese inside the roll and spoon the hot, saucy meatballs inside. Enjoy!
Notes
To make these in your slow cooker, make the meatballs as described above. Prepare the sauce in a skillet. Once it comes to a boil, pour the sauce into your slow cooker. Place the baked meatballs down in the sauce, and very gently turn them with a spatula in the sauce to coat them with it. Cover and cook on low for 4-5 hours. Serve as above. Note 2: Serve the meatballs on little buns and turn these into sliders!