Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large bowl, combine the ground chicken, breadcrumbs, Parmesan cheese, fresh parsley, minced garlic, beaten egg, salt, pepper, and red pepper flakes (if using). Mix until just combined; do not overwork the meat.
Shape the mixture into meatballs, about 1.5 inches in diameter, and place them on the prepared baking sheet.
Bake in the preheated oven for 18-20 minutes, or until the meatballs are cooked through and have a nice golden color.
While the meatballs are baking, prepare the honey garlic sauce. In a small saucepan, combine the honey, soy sauce, apple cider vinegar, and sesame oil. Heat over medium heat until the mixture begins to bubble slightly.
Reduce the heat and let the sauce simmer for about 3-5 minutes, allowing it to thicken slightly.
Once the meatballs are cooked, remove them from the oven and transfer them to a large mixing bowl. Pour the honey garlic sauce over the meatballs and gently toss to coat them evenly.
Serve the meatballs warm, garnished with sesame seeds and sliced green onions.