Put the onion, curry paste, chopped tomatoes, vegetable bouillon powder, ginger and yellow pepper into the slow cooker pot with a third of a can of water and stir well.
Add the chicken and push it under all the other ingredients so that it is completely submerged. Cover with the lid and chill in the fridge overnight.
The next day, cook on Low for 6 hrs until the chicken and vegetables are really tender. Stir in the coriander leaves just before serving over rice.