Preheat oven to 180°C. First roast the sweet potato. Chop the sweet potatoes into 3cm chunks. Spread over a baking tray. Drizzle with one tablespoon of the olive oil and season with salt and pepper. Put in the oven and bake for 25 minutes.
Meanwhile, peel and finely chop the red onions. Rip the stem from the chilli, cut it in half lengthways and remove the seeds, then finely chop. Peel and grate the garlic. Peel the ginger by scraping off the skin with a spoon and grate. Pluck the leaves from the coriander, put them to one side and thinly slice the stems. Roughly chop the dried apricots. Drain the chickpeas.
To make the tagine, place the saucepan over a medium heat and add the rest of the olive oil. Add the onions and fry for four to five minutes, stirring, until starting to soften. Add the chilli, garlic, ginger and chopped coriander stems and stir for two minutes. Add the harissa paste, ras el hanout, cumin, ground coriander and sugar and stir for one minute. Add the chopped tomatoes and water. Lower the heat and simmer for seven to nine minutes. Stir in the drained chickpeas and apricots. Put the lid on and simmer for eight to 10 minutes, stirring occasionally. Take the lid off the pan, taste and season. Add the coriander leaves and roasted sweet potato and stir. Reduce the heat to low and put the lid back on the pan.
To make the couscous, halve the preserved lemon and put it into a mixing bowl. Add the olive oil, cumin, couscous and boiling water. Cover with a dinner plate and set aside for eight to 10 minutes.
Meanwhile, spread the flaked almonds over a baking tray. Put in the oven and bake for four minutes, until lightly browned. Finely chop the coriander leaves.
Back to the couscous. Remove the preserved lemon and fluff the couscous with a fork. Reserve a quarter of the toasted almonds and a quarter of the chopped coriander leaves and fold the rest into the couscous. Taste and season with salt and pepper.
Divide the couscous among bowls and top with the tagine. Garnish with the reserved almonds and coriander and serve.