Place lemongrass, red onion, garlic, chillies. lime leaves, ginger and corn oil in a blender, blend for about 30 seconds. Then add the seasoning into the mixture and continue to blend to paste.
Prick chicken thigh with a fork for better absorption of marinade. Rub the paste on the chicken thigh all over evenly and marinate overnight.
Heat up oven pan with some oil. Place the chicken thigh (reserved the sauce) with skin on facing down and sear the skin to golden and turn over and fry for about 2 minutes. **alternatively can use a frying pan and a baking dish to bake the chicken if you don't have an oven baked pan.
Then place vegetables below the chicken thigh and pour in the remaining sauce with some shredded kaffir lime leaves and lemon grass on top.
Bake in preheated oven at 180 deg for about 45 minutes or a chopstick pierce through the chicken meat until the juices run clear.
Update: I've just checked with WMF SG that the oven pan that I bought is actually not suitable to place inside the oven for baking.