Combine butter, 2 teaspoons lemon juice, lemon peel, tarragon, mustard and salt in a small bowl. Stir until well blended and set aside. ( double this if using more than 3 pieces or more of fish)
Coat a nonstick skillet with cooking spray, heat over medium heat.
Drizle fish fillets with remaining 2 teaspoons lemon juice, sprinkle one side of each fillet with paprika.Place fillets in skillet, paprika side down, cook 3 minutes. Gently turn and cook 3 minutes longer or until fish begins to flake when tested with a fork. Place fillets on serving palte top with butter mixture.