Heat the oil in a pot over medium heat. Saute the onion and garlic for 1 - 2 minutes. Add beans, broth, tomato and rosemary and simmer for 20 - 25 minutes.
Take off heat and stir in lemon zest. Using an immersion blender or standup blender puree the soup until it is smooth. Garnish with parsley and serve with crackers.