Warm a pan over a medium heat (I use the same pan for all steps, so ensure it's big enough; cast iron is best to dry-fry the spices), without any oil, and add the cumin, coriander and mustard seeds. Cook them until they smell fragrant and start to pop.
Transfer them to a mortar (or spice mill), add the turmeric and grind until fairly smooth.
Dice the onions and the stalks from the chard.
Cook the chard leaves in some boiling water for approx 1-2minutes, until wilted. Remove and drain.
Heat a little oil in a pan and add the onions. Cook for a couple minutes then add the chard stalks. Cook, stirring now and then, for around 5-8mins until they have softened but are not browning.
Meanwhile, remove any fat and tough bits from the chicken and dice.
After the onions and chard are soft, add the chicken and brown. You may need to increase the temperature a little.
Once lightly browned, add the ground spices and grate in the garlic and ginger. Stir well.
Add ½ cup of coconut milk and stir.
Blend together the cashews and the remaining ¼ cup coconut milk then add to the pan.
Cook on a simmer rather than boiling for around 10 more minutes until the chicken is cooked.
Squeeze the chard leaves of excess water, cut fairly small then add to the pan and stir through.
Serve over rice.