In a medium bowl combine the chopped shrimp, mayonnaise, finely diced celery, and sliced green onion. Stir gently to combine without mashing the shrimp.

Add the lemon juice, Dijon mustard, Old Bay (or seafood seasoning), salt, black pepper, and minced chives if using. Fold everything together until evenly coated. Taste and adjust seasoning — add a little more lemon for brightness or a pinch more salt if needed.

Cover the bowl and refrigerate the shrimp salad for at least 15 minutes to let flavors meld. If you prepare it ahead, refrigerate up to 24 hours.

Toast and Assemble Roll

Heat a skillet or griddle over medium heat. Spread the softened butter evenly inside and on the top of the split roll (if using a split-top brioche, butter the cut faces and outer top).

Place the roll, buttered side down, on the skillet and toast until golden brown, about 1–2 minutes. Flip and toast the outside/top briefly to warm through, about 30–45 seconds. Remove from heat.

Place the lettuce leaf inside the warm roll to act as a barrier and add crunch.

Spoon the chilled shrimp salad into the roll, piling it gently but not overstuffing. For an even presentation, use a spatula to shape the filling so it sits neatly in the roll.

If desired, lightly sprinkle smoked paprika over the top for color. Serve immediately with a lemon wedge on the side for squeezing over the shrimp.