Heat your oven to 220°C/Fan 200°C/Gas 7. Pop the skewers in a dish or bowl of water (this helps stop them catching and burning under the grill).
Trim the green top off the aubergine and cut the aubergine into small cubes. Halve the pepper and scoop out the seeds and white bits. Roughly chop them. Trim the courgette, halve then quarter it lengthways and chop it into chunks to match the aubergine and pepper. Peel and chop the onion into chunky wedges.
Spread the veg out on a baking tray. Drizzle with 1 tbsp oil. Season and toss to coat and mix. Roast for 25-30 mins till soft and beginning to char.
While the veg roast, peel and crush the garlic. Scoop half into a medium bowl. Finely grate the zest from the lemon and set it to one side. Squeeze the juice from half the lemon into the bowl with the garlic. Add a pinch of the harissa (it’s spicy, so use as little or as much as you like) and the diced chicken. Stir to mix and set aside to marinate.
Scoop the remaining garlic into a small bowl and add the lemon zest. Finely chop the parsley leaves and stalks. Pop most of them into the bowl. Add 1 tsp cumin and 1 tbsp oil. Season with salt and pepper and whisk together with a fork. Set aside.
Heat your grill to medium-high and line a grill pan or baking tray with foil. Thread the chicken onto the skewers. Lay them on the tray and grill for 10-12 mins till the chicken is browned and cooked through. Turn every so often so they cook evenly.
While the skewers cook, pour the couscous into a heatproof bowl. Pour in 250ml boiling water. Cover with a saucer or cling film and set aside to soak.
Stir the couscous into the veg. Add the cumin and parsley dressing and toss to mix. Taste and adjust the seasoning if you think it needs it. Serve the veg couscous with the chicken skewers, scattered with the remaining chopped parsley and a pinch more harissa.