MAKE THE PATTY MIXTURE: In a large bowl, stir together the tuna, panko, onion, garlic, dill, Old Bay, salt, pepper, cayenne, lemon zest (if using) until well incorporated. In a measuring cup, whisk together the two eggs, mayonnaise, and Dijon-style mustard. Pour the egg mixture into the large bowl with the tuna mixture and mix well. Take a quarter cup or so of the patty mixture and pat it into a ball in your hands. If it seems dry and crumbly, return it to the bowl, and stir in another tablespoon of mayonnaise. If the ball holds together easily, proceed.