Heat oven to 200C/180C fan/gas 6. Toss the tomatoes in harissa and 2 tbsp of the oil. Season and spread in a roasting tin, cut-side up, and bake for 40-45 mins.
In a bowl, mix the soured cream, tahini and garlic oil with some seasoning. Set aside.
Tip the quinoa/maize couscous into a large bowl. Pour over 400ml boiling water. Cover with cling film and leave to stand for 10 mins or until all the water has been absorbed. Fork though the herbs. Top with the tomatoes and serve with a dollop of the cream sauce.