Preheat oven to 400 degrees. Place red potato on a baking sheet and pierce potato several times with a fork.
Transfer baking sheet to preheated oven and bake potato until tender (not mushy tender, just soft) about 35 minutes. Remove from oven and allow rest until cool enough to slice. Slice potatoes into about 1/4-inch thick slices.
Butter outsides of two slices of bread. Spread ranch dressing along opposite side of bread. Top one of the slices of bread (ranch side up) with sliced red potatoes followed by bacon, cheese and pepper to taste (I didn't think it needed any more salt because of the salt in the ranch, cheese and bacon but if you want to add some feel free).
Sprinkle green onions over ranch covered side of remaining slice of bread (so the onions have something to stick to) then top sandwich with that remaining slice (buttered side up).
Place in a 10-inch non-stick skillet, cover skillet and heat over medium-low heat. Cook for about 4 - 5 minutes until bottom is golden then carefully rotate to opposite side, cover and cook until bottom is golden, about 2 minutes longer. Serve immediately with more ranch dressing for dipping.
Notes
*For the ranch I actually just used the hidden valley ranch dressing mix, prepared according to directions on package and added a bit of fresh chopped basil and some dried parsley just to up the flavor a bit. I would just recommend using a good quality ranch, not the stuff from the shelf even the mix stuff is so much better than that kind. The refrigerated ranches near the produce are also better than that on the shelf (just my opinion I guess).