Prepare the couscous according to the package directions, omitting oil. Stir in tomato and allspice; keep warm.
Heat oil in a large nonstick skillet over medium-high heat. Add leek and next 6 ingredients (leek through garlic); sauté 8 minutes. Add spinach, parsley, sugar, salt, and chickpeas; sauté 2 minutes. Spoon the vegetable mixture over the couscous mixture, and serve with Harissa Sauce.