Thaw fish, if frozen. Rinse; pat dry with paper towels. Cut into 4 to 8 pieces. Set aside. Preheat oven to 450 degrees F. Line two baking sheets with foil; lightly coat with nonstick spray. In bowl combine chili powder, salt, dill, and pepper; set aside.
Scrub potatoes; cut in 1/2-inch thick wedges. In bowl toss potatoes with oil to coat. Add 1/2 teaspoon of the chili powder mixture; toss to coat. Arrange potatoes in single layer on one prepared baking sheet. Bake 10 minutes.
Meanwhile, pour buttermilk in shallow dish. In another shallow dish combine panko, garlic, and remaining chili powder mixture. Dip fish in buttermilk, turning to coat and allowing excess to drip off. Dip in panko mixture, coating both sides. Place fish on second baking sheet. Lightly coat with nonstick spray. Measure thickness.
Bake 4 to 6 minutes per 1/2-inch thickness of fish or until fish flakes easily when tested with fork and potatoes are tender. Sprinkle fish with fresh dill. Serve with vinegar. Makes 4 servings.