Preheat the oven to 180ºC / 350ºF / Gas Mark 4. Halve the peppers lengthways, brush with a little oil and place on a baking tray. Roast them for 10 minutes or until softened but still holding their shape.
Meanwhile, bring a small saucepan of water to the boil with the stock powder. Tip in the giant couscous and boil for 6-8 minutes until just cooked through.
Drain and return it to the saucepan, the squeeze over the juice of the lemon, and add the 2 tbsp olive oil and baby spinach leaves. Stir well and season well with salt and black pepper.
Heat a little oil in a frying pan, peel and finely chop the red onion and add to the pan. Cook for 3-4 minutes, then drain and rinse the chickpeas and add them to the pan, along with the tomato purée, harissa paste, boiling water and stock powder.
Bring to the boil then simmer for 5 minutes or until the liquid has reduced to a thick, sticky sauce. Taste and season as required.
To assemble, pile the giant couscous into the pepper halves, then top with the chickpeas. Return to the oven for 3-4 minutes to heat through, finely chop the coriander and sprinkle over the peppers, then serve immediately.