In a large bowl, combine ground chicken, bread crumbs, milk, egg, blue cheese, sliced onions, and 1/4 cup hot sauce. Reserve the remaining hot sauce.
Mix until ingredients are thoroughly incorporated; roll into 1 1/2 inch balls and place on a rimmed baking sheet.
Broil on low 4-5 minutes on each side, until lightly browned.
Transfer meatballs to a slow cooker; cover with hot sauce.
Cover slow cooker and heat on low 2-3 hours.
Garnish with crumbled blue cheese, ranch dressing, or blue cheese dressing as desired.