In a mixing bowl, combine buttermilk, fish sauce, red curry paste, garlic powder, and onion powder until smooth. Submerge the chicken in the marinade and refrigerate for at least 2 hours, preferably overnight.

In a shallow dish, mix together all-purpose flour, cornstarch, salt, and black pepper until well blended.

In a large frying pan, pour enough vegetable oil to cover the bottom by about half an inch, and heat over medium-high heat to 350°F (175°C).

Remove the chicken from the marinade, shake off excess liquid, and dredge each piece in the flour mixture.

Carefully place the dredged chicken in hot oil, frying for 6-8 minutes on each side until golden brown and reaching an internal temperature of 165°F (74°C).

In a small bowl, whisk together mayonnaise, sriracha, and lime juice until smooth. Adjust spice level to taste.

Lightly toast the brioche buns in a dry skillet over medium heat until golden.

Spread spicy mayo on the bottom half of each bun, layer with fried chicken, cabbage, pickled carrots, and cilantro, then top with the other half of the bun.

Serve immediately and enjoy!