Heat the olive oil over medium heat in a 3-4 quart Dutch oven or soup pot with a tight-fitting lid.
Add onion, garlic, cumin, and cinnamon, and season with salt and pepper.
Cook, stirring occasionally until the spices are aromatic and the onions are soft and translucent about 5 minutes.
Stir in squash and potatoes, season again with salt and pepper if needed, and cook until the vegetables are just starting beginning to soften - about 10 minutes.
Add the broth, chickpeas, tomatoes, and saffron, if using.
Bring the soup to a boil and then reduce heat to low. Cover and simmer on low for 30 minutes to an hour.
Prepare the couscous while the stew simmers.
Remove from heat and stir in zest and olives.
Serve the stew around a mound of couscous.