Peel and finely chop the onion. Warm a casserole, tagine or large pan over a medium-low heat for 2 mins. Add 2 tbsp olive oil and the onion. Season with a pinch of salt and pepper. Pop on the lid and gently sweat for 10 mins, stirring once or twice, till the onion has softened.
While the onion sweats, trim the courgettes, halve them and slice them into half-moons around 1cm thick. Peel the sweet potatoes and chop them into bite-size chunks. Stir the courgettes and sweet potatoes into the onion. Put the lid back on the pan and sweat for another 10 mins.
While the veg sweat, finely chop the dried apricots. Peel and grate or crush the garlic. Finely chop the coriander stalks (keep the leaves for later). Quarter the lemon to make 4 wedges. Drain the chickpeas and give them a good rinse.
Stir the apricots, garlic and coriander stalks into the veg. Add 2 tsp ground cumin, 1 tsp each turmeric and coriander seeds and drop in the cinnamon stick. Cook and stir for 1 min.
Tip the chickpeas into the pan and add the chopped tomatoes. Squeeze the lemon wedges over the pan to add in the juice, then drop the lemon wedges in too. Pour in 900ml boiling water. Pop a lid on the pan, turn the heat up and bring to the boil. Once it’s boiling, turn the heat down and simmer for 20 mins till the veg are tender.
Taste the tagine and add a pinch more salt or pepper if you think it needs it. Fish the cinnamon stick and the lemon wedges out of the tagine. Ladle it into warm bowls and serve garnished with the coriander leaves.