Flatten the chicken thighs out by lightly bashing them between two pieces of baking parchment with a rolling pin, then put in a sealable container with the garlic, paprika, chilli, ginger and a pinch of salt. Massage the mix into the meat, then chill until ready to cook for at least 1 hr or up to 24 hrs.
To pickle the cabbage, put the vinegar, sugar, coriander seeds and turmeric in a pan and bring to the boil to dissolve the sugar. Take off the heat and stir in the shredded cabbage, ensuring it’s completely immersed in the liquid. Cover and leave to cool.
For the relish, sprinkle the cucumber with a little salt and leave for 10 mins. Squeeze out the liquid, then stir the cucumber through the mayo and lime juice and set aside. For the glaze, mix the mustard and sriracha together in a separate bowl.
Heat a barbecue to medium or the grill to its highest setting. Barbecue or grill the chicken for 5 mins on one side, then flip and continue to cook, brushing with the glaze a few times until sticky, glossy and cooked through. Toast the buns, spoon some cabbage onto the base, place the chicken on top, then dollop a generous amount of the cooling cucumber relish over the chicken before closing the buns and serving.