Slit the chicken fillet from the middle and flatten each piece. You will get 4 thin chicken fillets from 500 g chicken.
Marinate the chicken with salt, white pepper, garlic powder, ginger powder, sriracha sauce and mustard sauce. Leave overnight or for 1 hour at least.
Make a batter with all the ingredients written under 'Batter'. Add the milk gradually and keep checking the consistency. The batter shouldn't be too runny. It should be able to stick to the chicken fillets.
Combine the 'Dry Mix' ingredients in a wide shallow bowl and keep aside.
Dip the chicken fillets in the batter first, then thoroughly coat with the dry flour mix. Press hard when dredging with flour and slide your fingers on it to create flakiness. Then dip the same fillet in batter followed by flour mix. We want two layers of for ultra-crunchiness.
Heat a pot with oil for deep-frying. On medium heat add the chicken fillets. Don't over crowd the pan, fry in batches. For the first 5 mins do not move the fillets. Cook the chicken for total 15 mins until cooked through. Don't forget to flip in between.
When done, take a big strainer and put chicken fillets on it. Use it to drain excess oil. This will prevent them from getting soggy.
Make a burger sauce by mixing all the sauce ingredients.
Start assembling your burger. Toast the buns. Take the bottom bun, on it put the crispy chicken, then 1-2 slices of cheese, couple of tomato slices, drizzle some of the burger sauce, add the salad leaf and close the burger with the top bun.
Serve with french fries and enjoy!