Set the oven at 400ºF/200ºC. Put the tomatoes (red, orange, yellow, green, cherry, etc.) into a roasting pan with the garlic and a little oil. Peel and slice the onion and add it to the tomatoes with a seasoning of salt and black pepper. Roast for twenty-five to thirty minutes until the tomatoes are soft and the skins lightly browned.
Bring the vegetable stock to a boil. Place the couscous in a heatproof bowl, then pour the boiling stock over, fold in the raisins, cover, and set aside for fifteen minutes. Roughly chop the mint and parsley leaves, discarding the stalks.
Use a fork to lightly crush the tomatoes so the juices bleed into the pan, then stir in the harissa paste. Toast the sesame seeds for a minute or two in a dry pan till golden. Stir most of the chopped herbs into the couscous with a fork. Serve the roasted tomatoes and their juices on top of the couscous, and sprinkle with the reserved herbs and sesame seeds.