Bake potatoes at 425° for 1 hour or until done; let cool slightly. Increase oven temperature to 475°.
Cut each potato in half lengthwise; scoop out pulp, leaving a 1/4-inch-thick shell. Reserve pulp for another use. Cut each shell lengthwise into four pieces.
Combine sour cream, 2 tablespoons salad dressing, and pepper; set aside.
Place potato shells on a baking sheet; spread shells evenly with horseradish mustard. Sprinkle evenly with cheese and top with crumbled bacon. Bake at 475° for 13 minutes or until shells are lightly browned and cheese melts.
Combine lettuce and remaining salad dressing; toss well. Place 2 cups lettuce mixture on each of six plates; top each with 4 potato pieces. Drizzle each with 1 tablespoon sour cream mixture and 2 teaspoons green onions.