Drizzle fillets with lemon juice; sprinkle with onion powder. Set aside.
In a microwave-safe dish, combine the shrimp, milk, celery, 1 tablespoon butter and parsley. Cover and microwave on high for 1 to 1-1/2 minutes or until celery is tender. Stir in bread cubes. Spoon shrimp mixture down center of each fillet. Starting with a short side, roll up and secure with toothpicks.
Place in a shallow microwave-safe dish coated with cooking spray. Brush with remaining butter; sprinkle with paprika. Cover and microwave on high for 3-5 minutes or until fish flakes easily with a fork. Let stand for 5 minutes before serving. Discard toothpicks. Yield: 2 servings.