Peel and finely chop the chillies and garlic. Combine the sugar, salt, sambal oelek, water, and rice vinegar in a pan and bring to a boil. Reduce the heat and simmer for about 8 minutes. Add the potato starch, stir and simmer for another two minutes – until it reaches a jam-like consistency.
Remove the meat from the chicken thighs and finely chop along with the chicken breasts. Peel the garlic. Chop fine along with the spring onions, lemongrass, gherkins, and half of the coriander. Zest the lemon and mix everything together with the soy sauce.
Heat the oil to 175°C in a large saucepan. Pre-heat the oven to 80°C. Pre-heat the grill to its highest setting.
Form two patties out of the chopped chicken and coat in panko. Carefully place the patties into the hot oil and fry for about 8 minutes. Set the patties on kitchen paper to drain and keep warm in the oven until time to serve.
Snap off the pak choi leaves, rub with oil and grill on all sides under the hot grill for about 5 minutes. Season with chilli sauce.
Slice the buns. Mix the mayonnaise and chilli powder and spread on both halves of the bun. Assemble the burgers with the pak choi, patties, sweet chilli sauce, krupuks and the rest of the coriander.