Preheat oven to 350°F. Scrub sweet potatoes and poke evenly with a fork. Place sweet potatoes on a baking sheet and bake for 60 minutes, or until soft.
Meanwhile, mix olive oil, lime juice, garlic, chipotle peppers, oregano, cumin, chili powder, salt and pepper in a medium bowl.
When sweet potatoes are done baking, allow to cool enough to handle. Cut them in half, lengthwise and scoop out some of the flesh, leaving about a 1cm (½") layer of flesh in the skin. Brush the skins with some chipotle mixture.
Raise oven temperature to 400°F and bake the skins for 5-10 more minutes, until crisp.
Wilt spinach in a non-stick skillet over medium heat. Add the spinach and black beans to the chipotle mixture and mix.
Stuff the sweet potato skins with the bean-spinach mixture. Top each skin with shredded cheddar. Place skins back in the oven for an additional 5-10 minutes, until cheese is melted.
Notes
Serve with a salad to make a complete meal. Make ahead: Complete recipe through step 3. Then put the skins in the fridge until ready to use.