Pop the skewers in a dish or bowl and cover with cold water. This will help stop them catching and burning while they cook. Set aside.
Peel the shallots and quarter them. Peel one of the garlic cloves and roughly chop it. Put them both in a small food processor or blender. Add 1 tsp each cumin and cinnamon. Spoon in half the Greek yogurt. Finely grate in the lemon zest and squeeze in the juice from half the lemon. Add a pinch of salt and pepper and whizz the mixture together. No food processor? Peel and grate the shallots and garlic, then stir with everything else.
Pour the marinade into a dish and add the chicken. Turn to coat. Set aside to marinate for 10-15 mins while you prepare everything else.
Peel and finely slice the red onion. Slice the pepper in half and dice one half, scraping out the seeds and white pith. Halve the cherry tomatoes. Peel and grate or crush the remaining garlic clove.
Warm ½ tbsp olive oil in a medium pan. Add the onion and diced pepper. Season with a good pinch of salt and pepper. Cook and stir for 5 mins to soften the veg. Stir in the garlic and halved cherry tomatoes. Tip in the couscous. Pour in 300ml boiling water. Bring to the boil, then take the pan off the heat and clamp on a lid. Set aside to soak for 15-20 mins – the couscous will suck up the water.
Heat your grill to high. Line a grill pan or baking tray with foil and rest a wire rack on it. Chop the remaining pepper half into chunks around 2cm across. Thread the marinated chicken and pepper chunks onto the skewers.
Lay the chicken shish kebabs on the wire rack and grill for 10-15 mins, turning them once or twice, till the chicken is golden brown all over and cooked through.
Fluff the couscous up with a fork and divide it between 2 warm plates. Add a handful of rocket to each plate and top with the chicken shish kebabs. Serve with the remaining yogurt on the side and the remaining lemon half sliced into wedges for squeezing.