Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large bowl, combine ground beef, ground pork, breadcrumbs, Parmesan cheese, garlic, egg, milk, Worcestershire sauce, salt, pepper, onion powder, and oregano. Mix until just combined—don’t overmix.
Roll the mixture into 1-inch meatballs and place them evenly on the prepared baking sheet.
Bake for 18-20 minutes, or until the meatballs are cooked through and slightly browned.
While the meatballs bake, prepare the sauce by whisking together barbecue sauce, grape jelly, soy sauce, Dijon mustard, and garlic powder in a saucepan over medium heat. Cook for 5 minutes, stirring occasionally, until smooth and heated through.
Transfer the baked meatballs to a slow cooker or serving dish. Pour the warm sauce over the meatballs and toss gently to coat.
If using a slow cooker, set to low heat and let the meatballs simmer for at least 2-3 hours for maximum flavor.
Serve warm with toothpicks or over rice for a heartier dish.