Cape Cod Lobster Roll

1 pound cooked and chilled Maine lobster meat, cut into large dice

1 mango, pitted and diced

1 small Thai chili, diced

1/4 cup freshly chopped flat-leaf parsley

1 teaspoon finely chopped tarragon leaves

1/4 cup mayonnaise

2 lemons, juiced

1 shallot, diced

1 stalk celery, diced

Salt and freshly ground black pepper

4 hot dog buns

4 leaves flat green lettuce