Preheat oven to 425°. Brush a large baking sheet with oil.
In a small saucepan over medium heat, combine butter, blue cheese, and hot sauce; season with salt. Cook, whisking frequently, until butter and cheese have melted, about 2 minutes. Let cool.
Meanwhile, in a medium bowl, stir celery, egg, garlic, bread crumbs, green onions, and onion powder; season with salt. Add chicken and half of hot sauce mixture and mix until combined.
Using a cookie scoop, portion chicken mixture into 1" balls and transfer to prepared sheet.
Bake meatballs until lightly golden, 15 to 17 minutes.
Toss meatballs in remaining Buffalo sauce and sprinkle with green onions.
