Preheat oven to 425 degrees. Bake the potatoes for 45 to 50 minutes, or until tender and cooked through when pierced with a sharp knife. Set aside to cool completely.
Once potatoes are completely cool, remove skins by peeling them off with your hands. If skins are difficult to remove, use a vegetable peeler. Chop potatoes into 1/2" pieces. Transfer to a large mixing bowl. Add shredded cheese, and green onion. Set aside.
In a small mixing bowl, combine the sour cream, mayonnaise, mustard, seasoning salt, and pepper. Pour dressing over the potato mixture and fold together gently until completely combined. Cover and refrigerate for at least 4 hours before serving.
Just before serving, gently fold the crumbled bacon into the mixture. Transfer mixture to a serving bowl and garnish with additional shredded cheddar and green onion, if desired.