Creating the Thai Fried Chicken Sandwich is simple when you follow these steps:

1. Marinate the Chicken: In a bowl, combine the buttermilk, fish sauce, soy sauce, sriracha, garlic powder, ginger powder, and black pepper. Add the chicken thighs, ensuring they are fully submerged. Cover and marinate in the refrigerator for at least 30 minutes or up to overnight.

2. Prepare the Coating: In a separate bowl, whisk together the flour and cornstarch. This mixture will give the chicken a crispy exterior.

3. Heat the Oil: In a deep skillet or frying pan, heat enough oil to submerge the chicken, about 2 inches deep, over medium-high heat.

4. Dredge the Chicken: Remove the chicken from the marinade, allowing excess liquid to drip off. Dredge each piece in the flour and cornstarch mixture, pressing gently to ensure even coating.

5. Fry the Chicken: Once the oil is hot, carefully add the coated chicken to the skillet. Fry each piece for about 5-7 minutes per side or until golden brown and cooked through. Use a meat thermometer to check that the internal temperature reaches 165°F (75°C).

6. Drain the Chicken: Remove the fried chicken from the oil and place it on a paper towel-lined plate to drain excess oil.

7. Toast the Buns: Lightly toast the burger buns in a separate pan or on a griddle until golden brown.

8. Assemble the Sandwich: On the bottom half of each bun, spread a layer of spicy mayo. Add a piece of fried chicken, followed by shredded cabbage, cilantro leaves, and sliced cucumber. Top with the other half of the bun.

9. Serve Immediately: Enjoy your Thai Fried Chicken Sandwich while it’s hot and crispy!