Add onion to a heated large saucepan. Dry saute over medium heat, 5 minutes, stirring once or twice, adding a bit of broth if necessary to keep from sticking. Add garlic, stir 1 minute.
Add bell pepper, sweet potato, and tomatoes with juice. Raise heat to medium high and simmer for 5 more minutes. Add garbanzo beans. Add salt, if desired and pepper to taste.
In a medium bowl whisk together the peanut butter and 1 cup broth until no lumps remain. Add spices. Stir into the vegetable mixture and add the remaining 3 cups of broth, bring to a simmer.
Cover pan with a lid, reduce heat to medium-low. Simmer 20-30 minutes, or until sweet potatoes are fork-tender.
Stir in the spinach and cook until the spinach is wilted. Just a few minutes. Taste for seasonings.
Ladle into bowls and top with roasted peanuts if using.
I serve this over, or alongside, cooked hot brown rice