1. Rinse chicken and pat dry; cut chicken into 1-inch chunks and sprinkle with about 1/8 teaspoon salt and 1/8 teaspoon pepper. Heat 1 tablespoon oil in a 12-inch frying pan (with 2- inch-high sides) or a 6-quart pan over medium-high heat. Add chicken and stir often until browned on the outside but still slightly pink in the center (cut to test), 3 to 4 minutes. Transfer chicken to a plate and add remaining tablespoon oil to frying pan.
2. Add onion and garlic to pan and stir often until onion is limp, about 5 minutes. Stir in cumin, coriander, turmeric, and cayenne and cook until spices are fragrant, about 1 minute. Add cauliflower, carrots, and chicken broth; bring to a boil. Lower heat, cover, and simmer until carrots are slightly tender when pierced, 10 minutes. Stir in bell pepper, zucchini, and tomatoes and simmer, uncovered, until zucchini is tender when pierced, 8 to 10 minutes longer. Add salt and pepper to taste.
3. Meanwhile, in a 3- to 4-quart pan over high heat, bring 2 cups water to a boil. Remove from heat, stir in couscous, cover, and let stand until water is absorbed, about 5 minutes.
4. Fluff couscous with fork and spoon onto a large serving platter. Spoon chicken and vegetables over couscous and sprinkle cilantro over the top.