Blend coriander leaves, ginger, garlic, onion, salt, coriander powder, cumin powder, red chilli sauce and 2 tbsps red curry paste to a smooth paste.
Add lemon juice and 2 tsps fish sauce and blend again. Transfer into a bowl, add chicken and mix well. Set aside to marinate for 1 hour.
Heat oil in a non stick pan. Add chicken along with the marinade and fresh red chillies. Cover and cook for 5-6 minutes.Dice cucumber.
Mix remaining red curry paste, ½ cup water and remaining fish sauce in another bowl.
Add cucumber to chicken and mix well. Spread rice over the chicken and pour red curry paste mixture on it.
Cover and cook for 10-12 minutes or till chicken is done. Switch off heat and let it stand for 7 minutes.
Garnish with mint sprig and serve hot.