Stuffed Sweet Potatoes with Chipotle Black Beans and Greens

Name: Stuffed Sweet Potatoes with Chipotle Black Beans and Greens
Ingredients: 4 smallish sweet potatoes (about 8 ounces each); 1 bunch (about 3/4 pound) chard, curly kale, or lacinato (dinosaur) kale; 1 tablespoon olive oil; 1 red onion, thinly sliced; Salt, to taste; 1-2 garlic cloves, minced; Zest and juice of 1 lime; 2-3 teaspoons minced chipotles in adobo, to taste; 1 (15 ounce) can black beans, drained and rinsed; Extra-virgin olive oil or melted butter, for drizzling; Crumbled queso fresco, for sprinkling (optional)