In a large mixing bowl, combine coconut milk, curry powder, minced garlic, grated ginger, salt, and sugar until well blended. Add the chicken thighs, ensuring they are fully submerged in the marinade. Cover the bowl and refrigerate for at least 1 hour, or ideally overnight.

On a large plate, mix together rice flour or cornstarch with salt and pepper for a well-seasoned coating. Remove marinated chicken from the refrigerator, let it drain briefly, then dredge in the mixture.

Heat oil in a deep skillet or fryer to 350°F (175°C). Carefully place coated chicken pieces into the hot oil and fry for 5-7 minutes per side until golden brown.

In a small bowl, whisk together the Thai chili sauce and plain yogurt until creamy. Set the sauce aside. Thinly slice the cucumbers and prepare the pickled carrots.

Toast the buns until golden and crispy. Spread a layer of sauce on each bun. Layer fried chicken, sliced cucumbers, pickled carrots, and fresh herbs. Top with the other half of the bun.

Garnish the sandwich with fresh cilantro, lime juice, or crushed peanuts. Serve immediately while the chicken is still warm and crispy.