Preheat oven to 400°. Slice potatoes into 1/2" coins.
In a large bowl, toss the potato rounds in olive oil. Season with salt, pepper, cayenne, and garlic powder, and toss until evenly coated. Place in a single layer on a large baking sheet. Bake for 30 to 40 minutes, until lightly browned and tender, flipping halfway through.
Top each potato round with cheese and bacon. Broil until melty, about 2 minutes.
Dollop sour cream onto each potato and garnish with green onions.