Combine soaked beans and 6 cups water in a saucepan. Bring to a boil. Reduce to a simmer and cook until beans are tender, about 45 minutes.
In a large pot, heat oil. Add onion, garlic and bell pepper. Stir fry until the onions are translucent.
Add cumin, tomato sauce, cayenne, lemon juice and 1/2 cup of the liquid from the beans. Reduce heat to a simmer and cook, stirring occasionally, for 15 minutes.
In a small bowl, combine peanut butter with 3/4 cup of the liquid from the cooked beans. Whisk together well.
Add to beans and stir to combine.
Add tomato mixture and stir to combine.
Bring to a boil. Reduce to a simmer and cook for 10 minutes, stirring occasionally.