Preheat the oven to 400 degrees with a rack in the center position.
Pierce each potato 4 times with a fork. Place the potatoes directly on the oven rack and bake until the skins are crisp and the flesh is fork-tender, 45 to 55 minutes. Let cool for about 10 minutes, until cool enough to handle. Turn the broiler to high.
Halve each potato lengthwise, then cut each half in half crosswise. Using a spoon, scoop out the flesh, leaving about 1/4 inch intact. Reserve the flesh for another use (or snack on it now).
Brush the skins on both sides with the olive oil and season with salt and pepper. Arrange them skin-side up on a baking sheet, spacing them apart, and broil until the skins start to crisp, 2 to 3 minutes, monitoring them closely so they don't burn. Flip the potato skins over and broil until the top edges just start to brown, 2 to 3 minutes more.
Reduce the oven temperature to 400 degrees. Push the skins together on the baking sheet so they are just touching. Top with the beans and corn. Drizzle the cheese sauce (or sprinkle the cheese) evenly over the top and bake until the cheese melts and ingredients are all warm, about 5 minutes.
Immediately garnish with the jalapeño, tomato, avocado, cilantro, scallions, and white onion if using. Season with salt. Serve warm, with lime wedges.