Preheat your oven to 400°F (200°C).
In a mixing bowl, combine the ground beef, breadcrumbs, chopped onion, parsley, egg, garlic powder, salt, and black pepper. Mix until just combined.
Form the mixture into meatballs, about 1 inch in diameter, and place them on a baking tray lined with parchment paper.
Bake the meatballs in the preheated oven for 15 minutes or until cooked through.
While the meatballs are baking, prepare the sauce. In a skillet over medium heat, combine the soy sauce, brown sugar, water, cornstarch, sesame oil, ginger, and red pepper flakes (if using). Whisk everything together until smooth.
Bring the sauce to a simmer, stirring constantly until it thickens (about 3-5 minutes).
Once the meatballs are done baking, add them to the skillet with the sauce, tossing to coat them well.
Cook for an additional 2-3 minutes to heat everything through.
Remove from heat and serve immediately over rice or noodles.