Preheat the oven to 375 degrees F (190 degrees C). Using the slicing side of a box grater, slice potato into thin rounds.
Line a baking sheet with parchment paper. Lay potato slices on the parchment paper to form a wide circle, slightly overlapping slices and ensuring no parchment is left uncovered. Drizzle slices with olive oil, then season lightly with salt and pepper.
Bake in the preheated oven until potatoes are slightly fork tender, 15 to 20 minutes. Remove from the oven. Cover potatoes with mozzarella cheese, then Cheddar. Return to the oven until cheese melts slightly, about 5 minutes. Remove from the oven and top with bacon. Return to the oven and let bake until cheese is completely melted, 5 to 6 minutes.
Remove and sprinkle with green onion. Let cool for 3 minutes before removing from parchment to a work surface. Cut into wedges.