Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it.
In a large bowl, combine the ground beef, panko breadcrumbs, eggs, minced garlic, chopped onion, soy sauce, hoisin sauce, sesame oil, grated ginger, black pepper, and salt. Mix until all ingredients are well combined, but do not overwork the mixture.
Form the mixture into meatballs, about 1 to 1.5 inches in diameter.
Place them on the prepared baking sheet, spaced slightly apart.
Bake in the preheated oven for 15-20 minutes, or until the meatballs are cooked through and nicely browned.
While the meatballs are baking, prepare the sauce. In a medium saucepan, combine the soy sauce, hoisin sauce, honey, rice vinegar, sesame oil, minced garlic, grated ginger, and red pepper flakes (if using).
Bring the mixture to a simmer over medium heat, stirring occasionally.
Add the cornstarch slurry to the sauce, stirring continuously until the sauce thickens. This should take about 2-3 minutes.
Once the meatballs are done baking, add them to the skillet with the sauce. Use tongs to gently turn and coat them on all sides. Alternatively, you can transfer them to a large bowl and pour the sticky sauce over the meatballs, gently tossing to coat them evenly.
Transfer the glazed meatballs to a serving platter. Garnish with chopped green onions and sesame seeds. Serve hot with rice, noodles, or as an appetizer.