Heat a large soup pot or Dutch oven over medium heat for a few minutes. Add oil then add cumin seed. Give them a quick stir then add the onion and garlic and cook until beginning to brown slightly.
Add the bell pepper and saute for 3 minutes.
Add the beans, corn, oregano, chipotle, salt and water. Bring to a boil, reduce heat, and simmer for about 15 to 20 minutes.
Transfer 1 cup of the beans and 1 cup of broth to a blender and puree with the tomato paste. Add back to the soup and stir.
Add cilantro, lime juice, avocado, spinach (if using), salt and pepper to taste. Stir to combine and serve hot.
Recipe Notes
Adapted from Great Vegetarian Cooking Under Pressure (1st ed.) by Lorna J. Sass (William Morrow Cookbooks, 1994).