Combine first 5 ingredients in a small bowl; stir well. Combine 2 tablespoons dillweed mixture and potato in a 13- x 9- x 2-inch baking dish coated with cooking spray; toss well. Spread potato in baking dish in a single layer. Bake, uncovered, at 350° for 20 minutes, stirring once.
Push potato to sides of baking dish, and arrange fish in center of dish. Drizzle 1/4 cup plus 2 tablespoons dillweed mixture over fish.
Snap off tough ends of asparagus spears. Remove scales from spears with a knife or vegetable peeler, if desired. Arrange asparagus over potato; drizzle with remaining dillweed mixture. Cover and bake at 350° 30 minutes or until fish flakes easily when tested with a fork. To serve, arrange fish, potato, and asparagus on individual plates.