Preheat the oven to 450° and line a sheet pan with a wire rack. In a shallow bowl, toss the bread crumbs, Parmesan, oil, garlic powder, salt and pepper to combine. In another shallow bowl, whisk the buttermilk and egg until smooth. In a third shallow bowl, spread out the flour.
Roll each asparagus spear in flour, then dip in the buttermilk mixture, letting the excess drip off. Then coat with the bread crumbs. Place each breaded asparagus on the wire rack. Bake until golden brown, 15 minutes, then transfer to a platter and serve with Dijon mustard.