Heat olive oil in a large saucepan or soup pot over medium heat. Add the leeks and garlic; saute until tender, about 5 minutes. Stir in the chicken broth, cannellini beans, bay leaves and cumin. Bring to a boil, then reduce the 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.
This makes a thick soup. Add additional broth if you prefer a thinner consistency.