Preheat your grill to medium heat. Scrub the sweet potatoes clean, pat dry, and pierce several times with a fork. Lightly brush with a teaspoon of oil and season with a pinch of salt.
Grill the sweet potatoes directly on the grate, turning occasionally, until the skins are blistered and the centers are tender when pierced with a fork (about 20–25 minutes, depending on size). If you prefer, bake the potatoes in a 425°F (220°C) oven instead, about 40–45 minutes, until tender.
While the potatoes cook, prepare the filling. In a bowl, combine black beans, corn, red onion, olive oil, smoked paprika, cumin, garlic powder, salt, and pepper. Toss gently so everything is coated and let flavors mingle for a few minutes.
When the potatoes are ready, remove them from the grill and let cool just enough to handle. Slice each potato in half lengthwise. Scoop out a portion of the flesh to create a shallow cavity, leaving a sturdy edge to hold the skins.
Mash the scooped potato flesh lightly with a fork for a creamy texture, then mix it back into the bean-corn filling so it stays moist and cohesive.
Fill each potato skin with the loaded mixture, mounding slightly. Return the filled skins to the grill for 3–5 minutes, just long enough to warm through and let the flavors fuse.
Remove from heat. Squeeze fresh lime juice over the tops, sprinkle with shredded cheese, and add a dollop of sour cream or Greek yogurt if using. Garnish with green onion and cilantro for a bright finish.