Slice double breast fillet in half and marinate with salt, caster sugar, sesame oil and Shaoxing wine. Place in refrigerator for 4-5 hours or overnight.
Take both marinated fillets out and let stand till it reaches room temperature.
Dust fillets with the mixture of Cornflour and Tapioca Flour. Fry each side for about 3-5 minutes (depending on the thickness and size of the fillets) until golden brown.
Drain on wire rack and let them rest while you prepare the lemon sauce.
Combine lemon juice, lemon zest, chicken stock, white vinegar, sweet sherry, caster sugar, Worcestershire sauce and longan syrup in a saucepan and heat over low heat till sugar dissolves.
Taste sauce and adjust accordingly (more sugar if you prefer it sweeter or lemon juice if you prefer it zing-ier).
Add in slurry and stir for another 1-2 minutes until the sauce thickens. Add in longans and turn heat off. Set sauce aside.
Slice chicken into strips and arrange on plate. Pour sauce over and garnish with sliced spring onions and chillies.