1. In a large saucepan, whisk together the tomato sauce, cumin, curry powder, 1/2 cup water, and 1/2 teaspoon each salt and pepper.
2. Stir in the tomatoes, onion, and eggplant and bring to a boil. Reduce heat and simmer, covered, until the eggplant is tender, 20 to 25 minutes.
3. Add the chickpeas and cook, uncovered, until the chickpeas are heated through and the mixture has slightly thickened, 4 to 5 minutes.
4. Meanwhile, prepare the couscous. Serve the stew over the couscous. Top with cilantro and a dollop of yogurt, if desired.