If sausage has casings remove them and crumble into pan with the ground beef. Brown both meats together until no longer pink. Drain fat.
Mix the salt, pepper, garlic powder and pepper flakes into the pizza sauce.
Put the browned meat and the seasoned sauce into the slow cooker and stir to combine. Cover and cook on low for 4 hours or on high for 1-2 hours, stir once or twice during cooking.
Preheat oven to 375 F. Cut the split French loaf into 3 separate sandwiches. Repeat with second loaf. If making all 12 servings, repeat with 3rd and 4th loaf.
Pull a small amount of bread out of the bottom of the loaf to make a bowl for the meat.
Fill the bowl with meat mixture.
Cover the meat mixture with shredded Mozzarella cheese.
Place the top of loaf onto the sandwich and wrap the entire thing in foil. Bake for 15 minutes in the oven and serve.