Heat your oven to 200°C/Fan 180°C/Gas 6. Scrub the sweet potatoes. Slice them into chips. Tip them into a bowl. Add ½ tbsp olive oil and some salt and pepper. Toss to coat in the oil. Spread the sweet potatoes fries out on a baking tray. Bake for 30 mins till the fries are tender and a little charred.
While the fries cook, peel and grate or crush the garlic into a bowl. Peel and grate in the ginger. Finely chop the dill stalks (keep the frondy leaves for later). Add them to the bowl. Finely grate in the lemon zest. Squeeze in the juice from half the lemon.
Stir in 1 tsp each ras el hanut and ground cumin. Add a pinch or two of dried chilli flakes (they're hot, so use as little or as much as you like). Stir in ½ tbsp olive oil and a little salt and pepper to make a thick paste.
Chop the chicken into bite-size pieces. Add to the bowl and turn to coat in the spice paste. Set aside while you make the salad.
Roughly chop the lettuce and tip it into a large bowl. Halve the cucumber, roughly chop it and add it to the lettuce. Peel and finely slice the onion and add to the bowl. Juice the remaining lemon half and whisk the juice with ½ tbsp olive oil and a little salt and pepper to make a dressing. Add to the salad and toss to mix.
Heat your grill to high. Line your grill pan or a baking tray with foil. Add the chicken to the pan. Grill for 10 mins, turning once or twice, till the chicken is golden and cooked through. Alternatively, you can fry the chicken for 10 mins, turning often, till cooked through.
Divide the salad between 2 serving plates. Top with the chicken. Chop the dill leaves and scatter them over the top. Serve the chicken shawarma salad with the sweet potato fries.