Combine the breadcrumbs, Italian seasoning, salt,
pepper, garlic, parsley, and mix.
Add in the egg and parmesan and mix until combined.
In the base of the slow cooker, add in the tomato sauce and break up the whole tomatoes.
Add in the red pepper, salt, black pepper, garlic cloves, parsley, basil, and stir.
Add in the mushrooms and onions and stir.
Form the meatballs between both palms and place them on top of the sauce.
Pour in more sauce on top of the meatballs.
Cook on low for 3 hours with the lid on.
Uncover and let it continue to cook for another hour and a half.
For the last half hour, cover the sauce again with the lid and let it finish cooking.