Preheat oven to 400℉Scrub potatoes and cut in half. If using full red potatoes, cut into quarters or 1 ½" dices.
Bring a pot of salted water to boil. Add potatoes and par boil for 8-10 minutes or until potatoes are just fork tender.
Drain potatoes well and place in a large bowl. Toss with salt and pepper then add ranch dressing and gently toss until potatoes are completely coated with ranch dressing.
Place potatoes in a greased 9x13" baking dish and spread potatoes out evenly. Bake in the preheated oven for 25 minutes.
Add cheese and bake another 5 minutes or until cheese is melted over the top. Garnish with green onion and serve hot.
