Marinate the chicken by combining buttermilk, fish sauce, red curry paste, garlic powder, and onion powder in a bowl. Submerge the chicken, cover, and refrigerate for at least 2 hours, preferably overnight.

Prepare the dredging station by mixing flour, cornstarch, salt, and pepper in a shallow dish.

Heat vegetable oil in a skillet to 350°F (175°C).

Dredge the marinated chicken in the flour mixture, ensuring an even coating.

Fry the chicken for 6-8 minutes on each side until golden brown and cooked through.

Make the spicy mayo by whisking together mayonnaise, sriracha, and lime juice.

Toast brioche buns until golden on the cut sides.

Assemble the sandwich with spicy mayo, fried chicken, cabbage, pickled carrots, and cilantro.

Serve immediately.