Heat the oven to 400°F. Lightly grease 8 cups of a standard muffin tin.
In a large bowl, combine the ground chicken, panko, egg, chopped celery, 1 tablespoon of the ranch dressing, 2 tablespoons of the Buffalo wing sauce, garlic powder, and salt. Mix gently until combined.
Divide the mixture among the 8 prepared muffin cups. Press it in lightly, leaving the tops rounded. Bake for 18 to 22 minutes, until the centers reach 165°F.
While the muffins bake, toss the sliced celery and shredded cabbage with the mayonnaise, apple cider vinegar, and remaining 1 tablespoon of ranch dressing.
Brush the tops of the cooked muffins with the remaining Buffalo wing sauce. Let them rest for 5 minutes, then serve with the celery slaw.