Heat oil in large saucepan over medium heat. Saute onion and garlic until tender (about 5 minutes). Stir in oregano, thyme, cumin, and pepper; cook one minute longer. Place half of beans in a blender and puree until smooth, adding chicken broth as needed to make a smooth puree. Add puree and remaning whole beans and broth to saucepan. Bring to a boil over medium heat, then simmer uncovered for 20-30 minutes. Serve garnished with diced tomatoes, and if desired, onion and shredded cheese.