Place ground beef, pepperoni, onions, garlic bread seasoning, pasta sauce, water, and half of the mozzarella cheese in a gallon size ziplock freezer bag. Place remaining mozzarella and parmesan cheese in sandwich size freezer bag. Freeze.
When ready to cook: Remove the sandwich bag of mozzarella and parmesan cheese from the freezer and place it in the refrigerator to thaw.
Place contents of gallon sized freezer bag into slow cooker. Cook on LOW for 6 hours. Break up meat with spatula.
Add uncooked pasta. Cook for 15-20 minutes longer, until pasta is cooked. Top with remaining mozzarella cheese. Cover and let cheese melt, 5 minutes.