Trim and pat the chicken pieces dry. In a bowl, combine buttermilk, soy sauce, garlic powder, onion powder and hot sauce. Submerge chicken in the marinade, cover and refrigerate for at least 2 hours or up to overnight.

Prepare Dredge

In a shallow bowl or wide dish whisk together flour, cornstarch, baking powder, salt, black pepper and paprika.

Dredge and Rest

Remove each piece of chicken from the marinade allowing excess to drip off. Dredge thoroughly in the flour mixture, pressing to form a good coating. Place on a wire rack and let rest 10–15 minutes to help coating adhere.

Fry

Heat about 1"–2" of neutral oil in a heavy skillet to 325–350°F (medium-high). If using a thermometer, maintain around 325°F for thighs. Carefully add chicken and fry in batches without crowding until golden brown and internal temperature reaches 165°F, about 6–9 minutes per side depending on thickness. Transfer to a wire rack set over a baking sheet to drain and keep warm in a 200°F oven if needed.

Kimchi Slaw

Drain chopped kimchi well (squeeze out excess liquid). In a bowl combine kimchi, sliced green cabbage, julienned carrot and scallions. In a small bowl whisk together mayonnaise, rice vinegar, sesame oil, sugar, salt and black pepper. Toss dressing into the cabbage mixture until evenly coated. Taste and adjust seasoning. Refrigerate until assembly.

Fried Onions

Separate the thin onion slices into rings. Toss lightly in the 1/2 cup flour and 1/2 tsp salt, shaking off excess. Heat 1/4–1/2" oil in a skillet over medium-high heat. Fry onions in batches, stirring occasionally, until golden brown and crisp, about 2–4 minutes. Remove to a paper towel-lined plate and season immediately with a pinch of salt. Keep warm or use at room temperature for assembly.

Cucumber & Assembly

Toast buns: heat a skillet over medium, spread butter on cut sides of buns and toast cut-side down until golden, about 1–2 minutes. Mix spicy mayo if using by combining mayonnaise with sriracha to taste (about 1:1 ratio or adjust).

Slice cucumber thinly and pat dry to remove excess moisture so sandwich doesn't get soggy.

Assemble: spread a layer of spicy mayo on the bottom bun, place the fried chicken piece on top, add a generous scoop of kimchi slaw, arrange sliced cucumbers, and top with a handful of fried onions. Cap with top bun and press gently. Repeat for second sandwich.

Steak Fries

If frying: heat oil in a deep pot to 350°F. Rinse cut potatoes to remove starch, then pat dry. Fry in batches until golden and cooked through, about 6–8 minutes. Drain on paper towels and season with salt, pepper and paprika. If baking: toss fries with 2 tbsp oil, salt, pepper and paprika, spread in a single layer on a baking sheet and roast at 425°F for 30–35 minutes, flipping once, until crisp and golden. Serve hot alongside sandwiches.