Heat oil in a medium, heavy bottom pot. Once the oil is hot, add onion, garlic and fennel along with a pinch of salt. Saute for 8-10 minutes or until the onion and fennel is beginning to look translucent.
Add tomatoes, broth, beans and season with salt and pepper, then bring to a boil. Once you've got your boil, reduce the heat and simmer for 20-30 minutes. This will allow the soup to thicken and become nice and hearty.
Once your soup has reached the desired consistency, stir in spinach. The spinach will wilt down in a matter of minutes and your soup will de done. Enjoy!