Put dates, pecan pieces, zest and sherry in the bowl of a food processor and pulse until it becomes a smooth, thick paste. Preheat your panini pan or press. Butter one side of each piece of bread. Spread a generous portion of the date spread on four pieces of bread (spread on the dry side). Top with turkey and then the second piece of buttered bread. Make sure the buttered side of the bread is facing outward. Place in your panini press or pan and cook until golden brown. Cut in half and serve immediately.