Toss the potatoes with olive oil and salt then spread in a single layer on a baking sheet.
Bake at 450 degrees until cooked through and slightly crisp, about 30 to 40 minutes.
Meanwhile cook the bacon and diced it up.
Transfer the cooked potatoes to a large mixing bowl. Reduce heat in the oven to 350 degrees.
Add in the ranch dressing, half the bacon, half the cheese and most of the onions. Toss well.
Add more ranch if needed and the remaining bacon.
Transfer to a large casserole dish and top with more cheese.
Bake until the cheese melts about 15 minutes.
Garnish with the remaining onions.
NOTE If cooking for a crowd, use a large aluminum pan to mix and bake the potatoes.