Pierce the chicken skin with a fork. Using the back of a knife, pound the breast to an even thickness.
Salt and pepper the breast, coat with soft flour and run it through the beaten egg.
Heat 1cm of oil in a medium skillet to 170C and add the chicken. Don't touch it until one side is golden, about 5 minutes, then flip. Remove when the other side is brown and crispy; drain the oil.
Wipe the skillet clean. Add the nanban sauce ingredients and bring to a boil over medium heat. Return the chicken and simmer, coating it all over.
Make the tartar sauce: mix all the ingredients well in a bowl.
Place the chicken over lettuce on a plate, top with plenty of tartar sauce and sprinkle with parsley.