Put oven rack in middle position and preheat oven to 375˚F.
Whisk together eggs, salt, and pepper until just combined.
Heat oil in an ovenproof 9-to 10-inch heavy nonstick skillet over high heat until very hot but not smoking. Add potatoes and scallions to oil, stirring once, then cover and cook until beginning to brown, about 4 minutes. Stir potato mixture once, then cover and cook 3 minutes more. Pour beaten eggs evenly over potato mixture and crumble cheese over eggs.
Transfer skillet to oven and bake frittata, uncovered, until set and just cooked through, about 15 minutes.
Invert a plate over skillet and, holding them together with oven mitts, invert frittata onto plate and serve immediately.