1. Preheat the oven to 375°F.
2. Place the squash, onion, carrots, and zucchini on a baking sheet and toss with olive oil, 1 teaspoon salt, and 1 teaspoon pepper.
3. Roast for 25 to 30 minutes, turning once with a spatula about midway through.
4. While the vegetables roast, bring the vegetable broth to a boil in a saucepan.
5. Remove the pan from the heat and stir in the butter, remaining 1/2 teaspoon pepper, cumin, saffron, and salt to taste.
6. Cover the pan and steep for 15 minutes.
7. Scrape the roasted vegetables and their juices into a large bowl, and add the couscous.
8. Bring the vegetable broth back to a boil, and pour over the couscous mixture all at once.
9. Cover tightly with a plate and allow to stand for 15 minutes.
10. Add the scallions, toss the couscous and vegetables with a fork, and serve.
