Heat oil in a large pot over medium heat. Add chopped onion and cook for 3-4 minutes until softened.
Add minced garlic and ginger, cooking for another minute until fragrant.
Add diced sweet potato, chopped greens, and tomato paste. Sauté for 2-3 minutes, stirring to coat vegetables.
Whisk in peanut butter, cumin, and cayenne (if using) until well combined.
Gradually add broth while stirring to prevent lumps from forming.
Bring mixture to a boil, then reduce heat and simmer for 15-20 minutes until sweet potatoes are fork-tender.
Season with salt and pepper to taste before serving.