Preheat oven to 400°F (200°C). Grease a 9×13-inch baking dish.
Toss diced potatoes with olive oil, salt, pepper, smoked paprika, garlic powder, and onion powder. Spread evenly in the baking dish and bake for 30 minutes, stirring halfway.
While potatoes roast, toss cubed chicken with half of the ranch dressing.
Remove potatoes from oven and reduce temperature to 350°F (175°C). Layer ranch-coated chicken over potatoes and drizzle with remaining ranch dressing.
Sprinkle cheddar cheese evenly over the top. Bake for 20–25 minutes until chicken is fully cooked and cheese is melted and bubbly.
Top with crumbled bacon and sliced green onions. Let rest briefly before serving warm.