Heat the oil in a large saucepan over medium heat. Add the onion and cook, stirring occasionally, until it starts to soften, 4 to 5 minutes.
Add the cumin, ginger, ½ teaspoon salt, and ¼ teaspoon pepper and cook, stirring, until fragrant, 1 minute.
Add the tomatoes (crushing with your hands as you add them) and their liquid, chickpeas, cauliflower, raisins, and ½ cup water and bring to a boil.
Reduce heat and simmer until the vegetables are tender and the liquid has slightly thickened, 15 to 20 minutes.
Fold in the spinach and cook until just wilted, 1 to 2 minutes.
Meanwhile, place the couscous in a large bowl. Add 1 cup of hot tap water, cover, and let sit for 5 minutes. Fluff with a fork. Serve with the stew.