In a bowl, toss the chicken with curry powder and oil until evenly coated. Set aside.
Add coconut cream, curry paste, peanut butter, kecap manis, and garlic to the slow cooker. Stir until smooth.
Heat a frying pan over medium high heat and cook the chicken for a few minutes on each side until lightly browned. Transfer to the slow cooker.
In the same pan, cook the onion until softened and starting to colour, then add it to the slow cooker and stir everything together.
Cover and cook on low for 6 hours or high for 3 hours. Add capsicum in the last hour of cooking.
Stir well before serving and spoon over rice. Garnish with chopped peanuts, coriander and red chilli, if using. Serve.