Heat the oven to 400°F. Lightly grease 8 cups of a standard muffin pan. Set a large pot of salted water over medium-high heat and bring it to a boil.
Add the cauliflower florets to the boiling water. Cook for 10 to 12 minutes, until very tender when pierced with a fork. Drain well and return the cauliflower to the pot.
While the cauliflower cooks, combine the ground chicken, egg, panko, ¼ cup of the buffalo sauce, diced celery, sliced scallion whites, garlic powder, salt, and black pepper in a mixing bowl. Mix gently until just combined.
Divide the chicken mixture among the 8 prepared muffin cups. Bake for 20 to 25 minutes, until the muffins are cooked through. Brush the tops with the remaining buffalo sauce during the last 5 minutes of baking.
Mash the drained cauliflower with the butter and milk until creamy. Spoon the mash onto plates, then top with the chicken muffins. Finish with the crumbled blue cheese and sliced scallion greens.