Place the chicken thighs into a shallow dish. Toast the cumin seeds in a small saucepan over a gentle heat, until they begin to 'pop'. Transfer them to a mortar and grind with the pestle to a coarse powder. Pop them into a bowl.
Open the cardamom pods and put the tiny black seeds into the mortar and crush with the pestle. Add them to the bowl with the cumin.
Stir in the honey, grated ginger, garlic, chili (if using) and 4 tablespoons of the olive oil. Season with salt and freshly ground black pepper and pour the mixture all over the chicken. Leave to marinate for a couple of hours if possible.
Heat the remaining olive oil in a frying pan, remove the chicken from the marinade and gently fry the chicken until golden brown all over. Transfer the browned chicken to the Tagine and pour over any leftover marinade. Scatter the onion slices over and pour in the stock. Stir in the drained chickpeas, chopped tomatoes and olives.
Put the lid onto the Tagine and cook in the oven at 375°F for one hour, until the chicken is tender. Stir in the chopped coriander and serve immediately with couscous or some plain boiled rice.