Preheat oven to 400 degrees and line a baking sheet with parchment paper.
Gently mix together almond meal (or bread crumbs), meat, Parmesan cheese, parsley, garlic, onions, eggs, salt and pepper.
Spray hands with cooking spray to make handling the meatballs easier. Use a 1 ½ inch scoop to ensure each meatball is the same size, and roll them by hand to give them a nice round shape before placing them evenly on the cookie sheet (this recipe should produce 36 meatballs).
Bake for about 20 minutes or until meatballs are cooked through. Leave the oven on 400 degrees.
Heat marinara sauce in a large heavy saucepan over medium heat. Drop meatballs into sauce, and bring to a gentle simmer. Cook, for 5 minutes.
Arrange sub rolls cut side up on a baking sheet. If the tops aren’t slit open, cut each one, being careful to only cut through the bun halfway.
Place 2 meatballs in each bun, and top with a spoonful of marinara, 1 tablespoon mozzarella, and 1 teaspoon Parmesan for each meatball.
Bake until cheese melts, about 3-4 minutes.
Remove and sprinkle with a little fresh parsley before serving.