In your large mixing bowl, combine the ground beef, breadcrumbs, grated Parmesan, chopped parsley, egg, garlic powder, onion powder, salt, and black pepper. Mix gently but thoroughly until just combined.
Divide the mixture into 16 even portions and roll each into a small, round ball about the size of a walnut. Place them on a plate or tray.
Preheat your oven to 400°F (200°C). Arrange the meatballs on a baking sheet lined with parchment paper or lightly greased. Bake for 15-18 minutes, turning once halfway through, until cooked through and golden brown. Alternatively, brown them in a skillet over medium heat, turning frequently until evenly cooked.
Once cooked, transfer the meatballs to a bowl and pour the sweet chili sauce over them. Stir gently to coat each meatball evenly with the sauce.
Slice your sub rolls open lengthwise but not all the way through, creating a pocket. Layer the bottom halves with shredded lettuce, diced tomatoes, and sliced jalapeños if using.
Spoon the saucy meatballs into each sub, distributing evenly. Sprinkle shredded mozzarella cheese on top. For melted cheese, place the assembled subs under the broiler for 2-3 minutes or in a hot oven until bubbly and golden.
Serve these Sweet Chili Meatball Subs immediately while warm. Enjoy with fries or a fresh salad for a complete meal.