Hollow out bun bottoms, leaving a 1/2-in. shell (save removed bread for another use). In a large skillet, heat butter over medium heat. Add shrimp; cook and stir 3-4 minutes or until shrimp turn pink., In a small bowl, mix mayonnaise, lemon juice, dill, salt and pepper until blended. Add shrimp; toss to coat. Spoon shrimp mixture into bun bottoms. If desired, top with lettuce and tomato. Replace bun tops.