Combine vinegar, sugar and mustard seeds in a small saucepan. Bring to a gentle boil, reduce heat and cook until sugar has dissolved. Remove from heat. Add cucumber to saucepan and allow mixture to cool completely.
Combine chicken, Five Tastes Curry Paste and kaffir lime leaf in a bowl to marinate. Meanwhile, heat a grill plate over high heat. Spray roti breads with oil and heat for 1-2 minutes on each side until warm and slightly grilled. Remove and keep warm.
Reduce heat to medium-low and heat oil. Add thigh fillets and cook for 5-6 minutes on each side or until cooked through. Remove and rest for 5-10 minutes.
Drain cucumber and thinly slice chicken.
To assemble, divide cucumber, coriander, shredded lettuce, spring onions, carrot and chicken between roti breads. Roll up and cut each into 4 pieces or desired size.