In a large pan fry off onion, capsicum, sweet potato, garlic, ginger and chilli gently in oil until vegetables soften.
Add the remaining spices, lentils and stock, bring to the boil, cover, lower heat and simmer 10 minutes, stirring often.
Add the spinach, stir and then place the chicken thighs in the sauce, cover and simmer gently for 20 minutes.
Turn the chicken over and continue cooking for 30-40 minutes or until the chicken is cooked through.
Stir in the coriander if using, and serve with steamed rice.