Mix the egg, garlic and lemon rind together in a shallow dish, add the chicken and leave to marinate for 10–15 minutes.
Remove the lemon rind and add the cornflour to the marinated chicken. Mix thoroughly to distribute the cornflour evenly among the chicken slices.
Heat the oil in a wok over a high heat until the oil starts to shimmer. Add the chicken slices, making sure you leave a little space between them, and fry for 2 minutes on each side.
Reduce the heat to medium and stir-fry for 1 more minute or until the chicken is browned and cooked. Turn up the heat and pour in the lemon juice. Add the spring onion, garnish with lemon slices and serve immediately.