Marinate Chicken:
Combine chicken, curry powder, salt, and oil in a large bowl, mixing well. Thread the chicken onto bamboo skewers and marinate for at least 10 minutes, or overnight if possible.
Cucumber Relish:
Dissolve sugar in vinegar and salt by boiling for 3-4 minutes, then cool. Mix cucumber, shallot, and chilli in a bowl and add the cooled vinegar mixture.
Satay Sauce:
Grind roasted peanuts finely using a mortar and pestle or food processor. In a saucepan, heat vegetable oil over medium heat, sauté curry paste until fragrant, then add coconut milk, roasted peanuts, peanut butter, fish sauce, and sugar. Cook for a minute, adjust seasoning, and keep warm.
Cooking:
Grill chicken skewers on a barbecue or in a non-stick pan over medium-high heat for 3-4 minutes per side or until done. Serve with warm satay sauce and Thai cucumber relish.