Preheat your oven to 400°F (200°C).
In a large mixing bowl, combine the ground beef, breadcrumbs, grated Parmesan, chopped green onions, minced garlic, egg, salt, black pepper, and red pepper flakes (if using). Mix until well combined.
Shape the mixture into meatballs, about 1 inch in diameter. Place the meatballs on a baking sheet lined with parchment paper.
Bake the meatballs in the preheated oven for 20 minutes or until they are cooked through and have reached an internal temperature of 160°F (70°C).
While the meatballs are baking, prepare the honey garlic sauce. In a small saucepan, combine honey, soy sauce, rice vinegar, and sesame oil. Whisk over medium heat until the mixture is well combined and slightly thickened, about 3-5 minutes.
Once the meatballs are done, remove them from the oven and place them in a large bowl. Pour the honey garlic sauce over the meatballs and toss until they are well coated.
Serve the honey garlic meatballs hot, garnished with sesame seeds and chopped cilantro if desired.