Trim lemongrass ends, and remove outer leaf. Chop finely.
Remove base of pak choi and cut into 2" pieces.
Peel garlic and ginger and finely chop. Chop chilli.
(Optional) Lightly fry off lemongrass, pak choi, garlic, chilli and ginger, in a little oil. After 1-2 minutes, place items in slow cooker.
(Optional) Brown chicken thighs in the same oil as used previously. When browned, place in slow cooker.
Dissolve the creamed coconut in a jug with 300ml boiling water and stir in the stock cube.
Pour coconut stock over chicken and close slow cooker. Set cooker to 3-4 hours on high, or as appropriate.
With 20 minutes to go, wash, top and tail sweetcorn, split down middle and add to slow cooker.
When timer goes, remove the larger bits of chicken from slow cooker to a warmed dish. Give the rest of the contents a stir, and add couscous. Allow the couscous to cook by the residual heat for 10 minutes, or until it has absorbed the liquid and is ready to eat.
Serve the couscous and coconut curry in dishes or deep plates, and top with pieces of chicken removed earlier.