Put a large dry pan on a low heat. Add 1 tsp cumin seeds and 1 tsp coriander seeds. Toast for 2-3 mins till the seeds start to pop and smell aromatic. Tip them into a pestle and mortar and grind them, or tip them into a bowl and roughly crush them with the bottom of a jam jar. Set aside.
Peel and finely chop the onion. Peel and dice the carrot. Trim and finely slice the celery. Warm 1 tbsp olive oil in a large pan. Add the onion, carrot and celery. Season with salt and pepper. Cook gently for 5 mins till the veg start to soften. Stir often and keep the heat low. If the veg look like they might stick, add a splash of water.
While the veg cook, peel and crush or chop the garlic. Add it to the veg with the crushed cumin and coriander. Add 1 tsp each ginger and turmeric, and ½-1 tsp harissa (it's spicy, so use as little or as much as you prefer). Drop in the cinnamon stick. Stir and fry for 1 min.
Drain and rinse the chickpeas. Stir them into the pan with the chopped tomatoes. Fill the tomato can with water (around 400ml) and add that to the pan too. Pop a lid on the pan.
Turn up the heat. Bring the stew to the boil then turn the heat down to low. Simmer for 20 mins, stirring every now and then. If the stew looks like it’s getting too thick, turn the heat down (if possible) and add another splash of water.
Finely chop the parsley. Stir half into the stew. Taste and season with salt and pepper if you think it needs it.
Ladle the stew into warm bowls. Top each bowl with 1 tbsp of the yogurt, then sprinkle with a pinch more harissa and the remaining parsley. Serve straight away.