While the potatoes roast, place the grated onion into the center of a clean cheesecloth or thin kitchen towel. Gather the ends and twist firmly to squeeze out as much moisture as possible — this is crucial to avoid soggy meatballs. In a large mixing bowl, combine the squeezed onion, ground chicken, minced garlic, garlic powder, onion powder, crumbled feta, chopped fresh mint, kosher salt, black pepper, egg, and breadcrumbs. Use your hands to gently mix until just combined, being careful not to overwork the meat.
1.5 lbs ground chicken, 1 medium yellow onion, 2 garlic cloves, ½ teaspoon garlic powder, ½ teaspoon onion powder, ¾ cup crumbled feta, 1 teaspoon salt, ¼ teaspoon black pepper, 1 egg, ½ cup breadcrumbs