In a large, high-sided skillet, heat the oil over medium-high heat. Add the onion and cook until softened, about 5 minutes. Add the garlic, carrots, bell pepper, stock, and spices and bring to a boil. Reduce to a simmer and cook for 10 minutes. Add the zucchini, eggplant, raisins, and half the cilantro and continue cooking until tender, about 25 to 30 minutes. Season to taste with salt.
Prepare the couscous according to the package instructions for 4 servings. Serve with the tagine garnished with the remaining cilantro.