Use a fork to whisk the egg white in a large bowl until foamy. Add the chicken in batches and toss to coat. (The egg whites may need to be whipped several times as the foam catches the chicken -- this is what makes the breading fluffy).

Place the combined flour, salt, Chinese five spice and pepper in a large shallow bowl.

To make the Thai dipping sauce, whisk the lime juice, sugar, sweet chilli sauce and fish sauce in a small serving bowl.

Heat the oil to 180°C in a large saucepan over medium-high heat (when the oil is ready, a cube of bread will turn golden brown in 15 seconds). Add one-quarter of the chicken to the flour mixture and toss to coat. Shake off excess. Add to the oil, 1 at a time, and cook for 2-3 minutes or until light golden and cooked through. Transfer to a plate lined with paper towel. Repeat, in 3 more batches, with the remaining chicken and flour mixture, reheating the oil between batches.

Arrange the lettuce on a serving platter and top with the chicken. Sprinkle with shallot and chilli, if desired. Serve with the Thai dipping sauce.