Heat the oven to 400°F. Prick each potato a few times with a fork. Rub with the oil and sprinkle with ½ teaspoon of salt.
Bake directly on the oven rack for 55–65 minutes, until a knife slides in easily. Let cool for 10 minutes.
Cut each potato in half lengthwise. Scoop the insides into a bowl, leaving about ¼ inch of potato in the skins. Set the shells on a sheet pan.
Mash the potato with the butter, sour cream and ¼ cup of milk until smooth, adding more milk if needed. Stir in 1 cup of the cheddar, half of the bacon, half of the green onions, ½ teaspoon of salt and the pepper.
Spoon the filling into the shells, mounding it up. Top with the remaining cheddar and bacon.
Bake for 15–20 minutes, until heated through and golden on top. Sprinkle with the remaining green onions.