Heat the oven to 375°F. Lightly grease 8 cups of a standard muffin pan.
In a large mixing bowl, combine the ground chicken, egg, breadcrumbs, buffalo sauce, cheddar, celery, green onion, garlic powder, and salt. Mix gently just until combined.
Divide the chicken mixture among the 8 prepared muffin cups. Press it lightly into each cup without packing it tightly.
In a small bowl, stir the crumbled cornbread with the melted butter. Sprinkle the crumble evenly over the meatloaf muffins, pressing gently so it stays in place.
Bake for 22 to 26 minutes, until the chicken is cooked through and the tops are golden. Let the muffins rest in the pan for 5 minutes before loosening the edges and serving. Offer extra buffalo sauce alongside.