Heat olive oil in a large stockpot over medium heat. Add the leeks and garlic; saut� until tender, about 5 minutes. Stir in the chicken broth, cannellini beans, bay leaves and cumin. Bring to a boil, reduce heat to low and stir in the couscous. Cover, and simmer for 5 minutes. Stir in spinach and season with salt and pepper. Serve immediately.