Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the ground beef, breadcrumbs, grated Parmesan cheese, chopped parsley, egg, garlic powder, onion powder, and a pinch of salt and pepper. Mix until well incorporated.
Scoop out portions of the mixture and roll them into 1-inch meatballs. Place each meatball on the prepared baking sheet with space between them.
Bake the meatballs in the preheated oven for 15-20 minutes, or until fully cooked and golden-brown.
While the meatballs are baking, heat the BBQ sauce in a saucepan over medium heat until warmed through.
Once the meatballs are cooked, transfer them to the saucepan with the BBQ sauce and stir gently to coat.
Cut each sub roll open along the top, ensuring not to slice all the way through. Optionally, toast them in the oven for about 5 minutes.
Fill each toasted sub roll with BBQ-coated meatballs, sprinkle shredded mozzarella cheese on top, and add pickled jalapeños if desired.
Return the filled subs to the oven for about 5 minutes, or until the mozzarella cheese is melted and bubbly.
Remove the subs from the oven and serve immediately, with extra BBQ sauce on the side for dipping.
Notes
Serve with extra BBQ sauce on the side for dipping.