Preheat oven to 400°F.
Grease a 9x13-inch baking dish.
Place diced potatoes in a large bowl. Toss with olive oil, salt, and pepper.
Spread potatoes into the prepared baking dish.
Bake for 30 minutes, stirring halfway through, until potatoes begin to soften.
While potatoes bake, combine sour cream, mayonnaise, ranch seasoning, cooked chicken, 1 cup cheddar cheese, half the bacon, and half the green onions in a large bowl.
Remove potatoes from the oven and reduce temperature to 375°F.
Add the chicken mixture to the potatoes and stir gently to combine.
Spread evenly in the baking dish.
Top with remaining cheese and bacon.
Bake for 20 minutes or until hot and bubbly.
Remove from oven and let rest for 5 minutes.
Sprinkle with remaining green onions before serving.