Cut the chicken with medium bite-size pieces. Season the chicken pieces with coconut milk, turmeric, chilli powder, curry powder, salt, and lemongrass. Mix well, set it aside and marinate for at least 1 hour. ( If you have more time you can leave it for more hours or keep it in the fridge overnight. )
Heat the skillet or grill pan over medium-high heat. Drizzle one tablespoon of oil and char the chicken for 2-3 minutes on each side. Set it aside and keep it warm.
Heat the pan into medium heat, add 2-3 tablespoons of oil, saute the onions until translucent, follow with chopped garlic and lemongrass and cook until the onions are slightly brown.
Then add the seasonings turmeric, chilli powder, and curry powder for few seconds.
Pour the coconut milk, water, and peanut butter. Season with salt and sugar. Stir it well and bring it to simmer.
Placed the grilled chicken pieces back in the curry sauce and cook with low-medium heat for 8-10 minutes until cooked through. ( If the sauce is too thick, add more water if needed. )
Make a taste test and add more salt or sugar to your taste.
Turn off the heat and add chopped spring onions and chilli slices.
Transfer to serving plate, topped with roasted crushed peanut, and chopped coriander. Simply serve it with plain rice, coconut rice, naan or flat bread.