In a large saucepan over medium heat, heat the oil. Add the onion, cumin, salt, and allspice and cook, stirring, until the onion is softened, about 3 minutes. Add the couscous and stir for 1 minute to toast lightly. Add the turmeric, pour in 1½ cups of water and bring to a boil. Reduce the heat, cover and simmer until couscous is tender, about 15 minutes. You should have about 4 cups.

Stir the chickpeas, grapes, and cilantro into the couscous. Transfer couscous-grape mixture into a large bowl, add the arugula and toss well. Serve warm or at room temperature with lemon wedges.