In the bottom of a slow cooker mix together crushed tomatoes, tomato paste, bay leaves, red pepper flakes, Italian seasoning, salt and pepper.
In a large bowl mix all of the meatballs ingredients together. Form into meatballs that are about the size of golf balls. Place into the slow cooker. Cover and cook on low for 4 hours or until fully cooked.
In a small bowl mix butter with garlic powder and dried parsley. Spread onto the cut sides of each sub roll. Lay the sub rolls open faced onto a baking sheet. Top each with 2 slices of provolone cheese. Place under the broiler in the oven until browned and the cheese has melted.
Remove from the oven. Top each sub roll with meatballs and sauce and serve immediately.