Preheat the oven to 200 degrees C. Place the tomatoes in a single layer in a baking dish (if necessary, cut a very thin sliver from the base of each tomato so that it will sit flat). Put the seeds and scooped-out flesh in a sieve over a jug, and press with the back of the spoon to squeeze out the juices. Discard the seeds and flesh.
Put the fruit in a small bowl with 1/3 cup (80ml) of the tomato juice. Stir, then leave to soak. Make up the remaining tomato juice to 350ml with stock.
Heat 2 teaspoons of the oil in a non-stick saucepan. Add the pine nuts and cook over a low heat, stirring all the time, for 2 minutes, until golden. Remove from the pan with a slotted spoon and set aside.
Add the remaining oil to the pan and cook the spring onions for 2 minutes, until soft. Stir in the spices and cook for a few more seconds. Pour in the stock and bring to a rapid boil. Remove from the heat, then add the couscous in a steady stream, stirring constantly. Cover and leave to stand for 3 minutes.
Stir the fruit, pine nuts and parsley into the couscous, then season. Spoon the couscous mixture into the tomatoes and replace the tops. Bake for 15 minutes until tender. Rest for 5 minutes before serving with yogurt or tzatziki.