Cut chicken breast into 3/4-1" cubes. Place in a small bowl and cover with buttermilk. Let soak 5-10 minutes (or as long as overnight).
Preheat oven to 450 degrees F. Line a heavy baking sheet with parchment paper and place 2 tablespoons butter in the center. Place in the oven while it preheats.
In a medium bowl, whisk together Panko, flour, salt, pepper and garlic powder.
Remove chicken from buttermilk and dredge in Panko mixture.
Remove hot pan from oven and brush melted butter to cover an area of the parchment large enough to fit all of the chicken without it touching.
Place the chicken pieces on the buttered parchment. Bake for 10 minutes, then flip and bake for 5 more minutes until golden brown.
Remove from the oven and toss with sauce in a medium bowl. Serve.