Preheat broiler. Whisk eggs in medium bowl to blend. Mix in corn, cheese and 2 tablespoons cilantro. Sprinkle with salt and pepper. Mix in tortillas.
Heat oil in heavy medium broilerproof nonstick skillet over medium-high heat. Add onion and sauté until just tender, about 5 minutes. Pour egg mixture into skillet and stir to blend. Cover skillet. Cook frittata over low heat until eggs are almost set, about 8 minutes. Uncover skillet; broil frittata until top is set and starting to brown, about 1 minute. Slide frittata onto plate. Sprinkle with remaining 1 tablespoon cilantro. Cut into wedges and serve.