For the curry paste: Combine all the ingredients in a small bowl and whisk together.
Place the onion, garlic and ginger in a slow cooker (5 litre capacity). Add the chicken pieces and then the paste. Stir well to combine. Cook on high for 4 hours.
After 3 hours, add the zucchini and cauliflower, if using. Stir well.
After 4 hours, turn off and add the greek yoghurt, lime juice, brown sugar and spinach (if using). Stir well to combine.
Serve on rice with toasted roti or naan bread and fresh coriander.
If you don’t have the time to make the paste, you can use a store bought butter chicken or tikka masala curry paste.With the yoghurt, you can either add it to the whole dish at the end, or hold off and just add a dollop on top of each bowl.