Heat the oven to 425°F. Line a rimmed baking sheet with parchment paper. Pierce each sweet potato several times with a fork and place on the sheet.

Bake for 50 to 60 minutes, until a knife slides easily through the thickest part and the centers feel soft. Large sweet potatoes may need another 10 to 15 minutes.

During the final 15 minutes of roasting, heat the olive oil in a large skillet over medium heat. Add the yellow onion and red bell pepper. Cook for 6 to 8 minutes, stirring, until tender.

Stir in the black beans, frozen corn, ground cumin, smoked paprika, 1/2 teaspoon of the fine salt, and water. Cook for 5 minutes, stirring occasionally, until hot throughout and most of the water has evaporated.

Remove the skillet from the heat and stir in the fresh lime juice. Taste and adjust seasoning as needed.

Carefully split the hot sweet potatoes lengthwise without cutting all the way through. Fluff the flesh with a fork and divide the remaining 1/4 teaspoon fine salt among them.

Spoon the warm bean mixture into the sweet potatoes. Top with the diced avocado and fresh cilantro, then serve while the filling is hot.