Place beans, yogurt, lime juice, cumin, oregano, garlic powder, paprika, salt and pepper in a food processor or blender. Process until well combined, about 20 seconds. For a spicier dip, add cayenne (or ground chipotle) to taste, up to 1/4 teaspoon. Add oil, cilantro (or scallions) and onion. Pulse until well mixed, about 20 seconds. Transfer to a bowl to serve.