Add chicken, buttermilk, fish sauce, soy sauce, lime juice, garlic and chili paste. Mix gently and let rest for at least thirty minutes in the fridge.

In another bowl, mix flour, cornstarch, salt and pepper together very well. This blend helps make a crisp and light crust.

Pour oil into a deep skillet or pot. Warm slowly over medium heat until bubbles form around a wooden spoon tip.

Remove chicken from marinade. Let excess drip off. Press each piece into the flour mix. Coat fully for crunchy texture after frying.

Place chicken pieces gently into hot oil. Cook in batches until golden and cooked through. Remove and drain on paper towels.

In a small bowl, mix mayonnaise, sweet chili sauce, and lime juice. Stir until smooth. This becomes your creamy Thai sandwich spread.

Combine cabbage, carrot, and cilantro in a bowl. Add a little lime juice and pinch of salt. Toss lightly for fresh crunch.

Lightly toast buns in a pan or toaster. Warm buns hold fillings better and keep texture crisp and pleasant.

Spread sauce on both sides of buns. Add fried chicken, slaw and cucumber slices if using. Place top bun and press gently.

Serve while hot and crispy. The contrast of crunchy chicken and cool slaw gives amazing flavor and texture in each bite.