Prepare all of the ingredients. Preheat oven to 400deg.
In a bowl, combine beef, pork, egg, pork rinds, 1 cup mozzarella, and parsley. Form into 1-inch balls and line out on a parchment paper lined baking sheet. Place in oven for 15 minutes.
In a large saute pan over medium heat, add butter. Once melted add garlic and onions. Cook for 5 minutes then add broth salt and pepper. Let cook until meatballs are done.
Brush inside of sub rolls with avocado oil and line up on a baking sheet. Once meatballs are out of oven - increase oven temp to 450deg. Put bread in to toast for 5-7 minutes.
Add meatballs to onion mixture, sprinkle with remaining cheese and cover with lid. Let cook while bread is toasting.
Add 4-5 meatballs on each sub, picking up onions as you get each one. Cut in half on the diagonal to serve.