The greens-to-egg ratio here is high, making this healthy as well as delicious. Slideshow: Healthy Egg Recipes
Preheat the broiler and position a rack 6 inches from the heat. In a large bowl, whisk the eggs with the Manchego and fold in the greens. Season with salt and pepper.
In a large ovenproof nonstick skillet, heat the oil. Add the eggs and cook over moderate heat until they’re lightly browned and nearly set on the bottom and side, about 3 minutes. Broil for 1 to 2 minutes, until the eggs are set and lightly browned on top. Slide the frittata onto a large plate, cut into wedges and serve hot or warm.