Pour the couscous into the bottom of a 16-ounce lidded heat-safe container, and top with the chickpeas, tomatoes, olives, carrots, cilantro, butter, curry powder, a heaping 1/4 teaspoon salt and harissa if using. Put the lemon wedge on top. Secure the lid, and refrigerate up to overnight.
When ready to eat, remove the lemon wedge and set aside. Add 1/2 cup boiling water to the container, and stir just to allow the water to reach the bottom. Cover, and let sit until the couscous absorbs all the liquid, about 6 minutes. Uncover, squeeze the lemon wedge over the couscous and stir again. Eat hot.
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