Heat the oven to 425 degrees F and arrange a rack in the upper third. Place potatoes on a baking sheet, drizzle with oil, season with salt, and toss to coat. Roast until potatoes are fork tender, about 30 minutes.
Set potatoes aside until cool enough to handle. Meanwhile, heat a medium nonstick frying pan to medium heat and cook chorizo, stirring occasionally, until browned, about 5 minutes. Set aside.
Slice potatoes in half and, using a melon baler or small spoon, scoop out most of the interior (leave about 1/4-inch of potato flesh). Divide chorizo among the skins and top with cheese. Bake until skins are warmed through and cheese is melted, about 5 minutes. Remove from oven, garnish with green onions, and pass sour cream on the side.