Add the couscous to a large bowl, sprinkle with a pinch of salt and the dried oregano, then pour over enough boiling water to cover. Use about 1¼ cups (300 ml) of water for 1 cup of couscous, or slightly more if you like it softer. Cover the bowl and let the couscous sit for 10–20 minutes, then fluff with a fork.
While the couscous is resting, dice all the vegetables into small pieces. Heat a generous drizzle of olive oil in a large skillet. Add the onion, carrot and celery and sauté until they start to soften.
Add the zucchini and bell peppers to the skillet and cook for a few minutes, stirring occasionally. Then add the eggplant and tomatoes, reduce the heat and let the vegetables stew gently for about 20 minutes, until tender and saucy.
Season the vegetables with salt and freshly ground black pepper to taste and let them cook for another 5 minutes. Turn off the heat, add the fluffed couscous to the skillet and gently mix until well combined.
Just before serving, stir in the chopped parsley and garnish with fresh basil leaves. Serve warm as a light vegetarian main or as a side dish.