Choose striped or uniquely colored heirloom tomatoes for this light vegetarian entrée or side dish. Add a drained can of tuna or salmon to the couscous filling, if you like.
Using a spoon, scoop out the middle of each tomato half, leaving ¼-inch flesh around the outside. Finely chop any large pieces and transfer to a large, nonreactive bowl, along with any accumulated juices. (Transfer the hollowed out tomato halves to a platter, cover, and set aside at room temperature.)
To the chopped tomato, add the couscous, vinegar, 1 teaspoon of the thyme, salt, and pepper. Stir well, cover and set aside at room temperature until the couscous is tender, about 1 hour.
Fluff the couscous mixture with a fork and then stir in the chickpeas. Spoon into the tomato halves, garnish with the remaining thyme, and serve.