Preheat the oven to 350°. Cook potatoes according to package directions. Add Parmesan cheese and 1 c. cheddar cheese to the potatoes and stir together. Place hot potatoes in an 8x8 or 9x9 glass baking dish and bake for 25 minutes.
Top with remaining cheddar cheese and bacon crumbles. Bake 5 more minutes, or until cheese is melted. Top with green onions and serve.