If you're chicken breasts are very large, halve them horizontally (resulting in two thin fillets).
Mix together the buttermilk and hot sauce then add the chicken.
Allow to marinate for at least 30 minutes but ideally overnight in the fridge. In a separate bowl, whisk the flour and spices together.
Add 3 tablespoons of the buttermilk mixture to the the flour and stir in with a fork.
Remove the chicken from the buttermilk and allow the excess to drip off. Coat the chicken in the flour mixture, making sure to really press the flour onto the chicken to coat it properly.
Thinly slice the cabbage, spring onion and jalapeño. Right before assembling the sandwiches, dress the slaw with lime juice and salt. If you do this too early, the slaw will become soggy.
Heat enough vegetable oil in a pot to deep fry the chicken (approximately 6 cups). Once hot, add the chicken and fry for 5-7 minutes until the chicken is golden brown, crisp and cooked through. Chicken is cooked when a meat thermometer reads 165°F/74°C.
Carefully remove the chicken from the oil and drain on paper towels.
While the chicken is frying, toast the buns in a hot pan. Add mayo to the bun then top with the fried chicken, a cheese slice and a generous spoonful of slaw. Sandwich with the top bun and serve immediately.