Preheat oven to 425°.
Snap off tough ends of asparagus. Cut asparagus into 2-inch pieces. Toss asparagus and peppers with olive oil, and place on a jelly roll pan coated with cooking spray. Bake at 425° for 8 to 10 minutes or until crisp-tender, stirring occasionally. Remove from oven. Sprinkle with lemon juice, 3/4 teaspoon dill, and 1/4 teaspoon salt, tossing gently to coat. Set aside, and keep warm.
Arrange fillets on a jelly roll pan coated with cooking spray. Sprinkle fillets evenly with remaining 1/4 teaspoon dill, remaining 1/4 teaspoon salt, and black pepper. Bake at 425° for 10 to 12 minutes or until fish flakes easily when tested with a fork. Top with asparagus mixture. Serve immediately.