In a mixing bowl, combine ground beef (or chicken), breadcrumbs, egg, garlic, ginger, green onions, soy sauce, black pepper, and sesame oil.
Mix until just combined (don’t overwork the meat).
Roll into 1-inch balls and place on a tray.
Heat a large skillet over medium heat with a drizzle of oil.
Cook meatballs until browned on all sides and cooked through (about 10–12 minutes). Remove and set aside.
In the same pan, add soy sauce, brown sugar, rice vinegar, hoisin sauce, garlic, ginger, and water.
Bring to a simmer, then add cornstarch slurry to thicken. Stir until glossy.
Add the cooked meatballs into the sauce, tossing to coat well.
Garnish with sesame seeds and fresh herbs.