Heat the oil in a large pot over medium heat. Add the onion and cook until softened, about 5 minutes.
Add the garlic and ginger, and cook for another minute.
Add the bell pepper and sweet potato, and cook for 5 minutes.
Stir in the diced tomatoes, vegetable broth, peanut butter, cumin, and cayenne pepper. Bring to a simmer and cook until the sweet potato is tender, about 15 minutes.
Season with salt and pepper to taste. Stir in the spinach and cook until wilted, about 2 minutes.
Serve the stew garnished with chopped peanuts and lime wedges.