Heat your oven to 200°C/Fan 180°C/Gas 6. Line a baking tray with baking paper. Drain the chickpeas and tip them into a bowl. Add ½ tbsp olive oil and toss to coat the chickpeas in the oil. Add 1 tsp each ground cumin and ground coriander with a good pinch of salt and pepper. Toss again to coat in the spices.
Peel and crush or grate the garlic. Halve the chilli, scoop out the seeds and white membrane, and finely chop them. Finely grate the zest off the lemon. Add the garlic, chilli and lemon zest to the chickpeas. Turn to coat well in the spices.
Spread the chickpeas out on a baking tray and slide into the oven. Roast for 25 mins till the chickpeas are crisp and have darkened a little.
While the chickpeas roast, tip the couscous into a heatproof bowl. Tip in the couscous and pour in 150ml boiling water. Add a little pinch of salt, swirl to mix, then cover the bowl with a plate. Set aside to soak – the couscous will absorb the water and swell, ‘cooking’ it.
While the couscous soaks, quarter the cherry vine tomatoes and pop them in a bowl. Peel and finely slice the shallots. Add them to the tomatoes. Finely chop the parsley leaves. Add them to the tomatoes too. Add 1 tsp sumach, the juice of half the lemon and ½ tbsp olive oil with a pinch of salt. Gently stir to mix. Set aside.
When the chickpeas are crisp and dark brown, take them out of the oven. Fluff the couscous with a fork and divide between 2 warm bowls or plates. Top with handfuls of lamb’s lettuce, the sumach tomato salad and the roast chickpeas. Serve with wedges of the remaining lemon, for squeezing.