Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan cheese, parsley, egg, garlic powder, onion powder, salt, and pepper. Mix well until all ingredients are fully incorporated.
Shape the mixture into 1-inch meatballs and place them on the prepared baking sheet.
Bake the meatballs in the preheated oven for 15-20 minutes, or until they are cooked through 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 done, remove them from the oven and transfer them to the saucepan with BBQ sauce. Stir gently to coat the meatballs in the sauce.
Cut the sub rolls open but not completely through. Lightly toast them in the oven for 5 minutes if desired.
Fill each sub roll with a generous amount of BBQ meatballs. Top with shredded mozzarella cheese and pickled jalapeños if using.
Return the filled subs to the oven for an additional 5 minutes, or until the cheese is melted and bubbly.
Serve immediately with extra BBQ sauce on the side for dipping.