Preheat the oven to 400°F.
In a large bowl, combine ground chicken, breadcrumbs, cilantro, garlic, ginger, soy sauce, fish sauce, lime juice, red curry paste, salt, and pepper. Mix until well combined.
Form the mixture into small meatballs, about 1 inch in diameter.
Heat vegetable oil in a large oven-safe skillet over medium heat. Add the meatballs in batches, cooking until browned on all sides, about 5 minutes.
Transfer the skillet to the oven and bake for 10-12 minutes, or until cooked through.
While the meatballs are baking, prepare the Khao Soi soup. In a large pot, combine chicken broth, coconut milk, red curry paste, soy sauce, fish sauce, lime juice, and brown sugar. Bring to a simmer over medium heat and cook for 10 minutes.
Once the meatballs are done, add them to the soup and stir to combine.
Serve hot over cooked egg noodles or rice, garnished with fresh cilantro, lime wedges, and chopped green onions.