1) Preheat oven to 220C/Gas 7.
2) Place chicken in a bowl and season with grill seasoning. Add egg, half of the grated cheese, bread crumbs, parsley, and a serious drizzle of extra-virgin olive oil to the bowl. Mix the meat and form 12 large meatballs. Squish the balls to flatten them a bit like mini oval meatloaves. Be careful not to form the balls wider than your bread. The flattened balls will stay put on your sub, no roll-aways! Bake the meatballs 15 minutes until golden and firm. Switch the grill on.
3) While the meatballs bake, heat a medium skillet over medium heat. Add 3 tbsp extra-virgin olive oil and garlic and cook 5 minutes then remove the cloves. Add crushed red pepper flakes then tomatoes and stir in the chicken stock. Season the sauce with salt and pepper and simmer 10 minutes, adjust seasonings and stir in the basil. Reserve a extra sauce for dipping on dinner table.
4) Remove the meat from oven and loosen with a thin spatula. Turn meat balls in sauce.
5) Cut sub rolls making the bottom a little deeper than the top. Hollow out a little bread and lightly toast the sub rolls under grill. Fill the bottoms of the breads with flattened balls and sauce. Combine the provolone and remaining Parmigiano. Cover the subs with cheese and return to grill to melt the cheese until golden.