Preheat the oven to 180C/350F/Gas 4.
For the couscous, toast the couscous grains in a dry hot pan for 1-2 minutes, or until lightly golden, shaking the pan frequently to prevent burning.
Transfer the couscous to a bowl and add the vegetable stock. Cover with cling film and allow to soak for 5-7 minutes, or until all the liquid is absorbed. Fluff up the grains with a fork and stir in the coriander and tomatoes.
For the lamb cutlet, heat the oil in an ovenproof pan and add the lamb and garlic cloves. Cook the lamb for 1-2 minutes on both sides, or until browned all over. Add the herbs to the pan, then transfer to the oven to cook for 5-7 minutes, or until the lamb is cooked to your liking.
For the rosemary butter, combine the butter and rosemary in a bowl and place in the fridge to chill before serving.
For the roasted tomato sauce, heat the oil in a frying pan, add the tomatoes and garlic and fry for 3-4 minutes, or until the tomatoes begin to burst. Season, to taste, with salt and freshly ground black pepper.
To serve, place a chefs' ring in the middle of a serving plate and pack in the couscous. Carefully remove the ring, then gently place the grilled lamb cutlet on top. Place a knob of the rosemary butter on top of the lamb, then spoon some of the tomato sauce around the edge of the plate.