In a bowl, cover the chicken thighs with buttermilk.
Add the bread crumbs / corn flakes, 2 tsp of Spice Bag spice mix, all of the flour and a pinch of black pepper to a plate or bowl and mix well.
Lift each chicken thigh piece with tongs, allowing any excess buttermilk to drip off and toss in the breadcrumb/spice mix, leaving each aside on a plate once coated.
Line the air fryer with a sheet of parchment paper and add in the chicken thigh pieces, spraying all over with the oil.
Cook for 15 mins until cooked through. Flip once close to the end.
Place a large frying pan over a high heat and once smoking, add the vegetable oil. When the oil is hot, add the Harissa chilli paste and onion rings and stir-fry for 3–5 minutes until the onions are tender and translucent, before pouring in the Shaoxing wine and sesame oil. Sprinkle with a teaspoon of the spice mix.
To assemble, slather toasted burger bun with mayonaise and add some shredded lettuce. Place a piece of chicken on top, along with a spoon of the fried onion and top with bun lids.
Notes
Based on this one from RTE = https://www.rte.ie/lifestyle/recipes/2023/1214/1421997-donal-skehans-spice-bag-chicken-buns/