How to Make It
Preheat the oven to 350°. In a bowl, toss the bread with 2 tablespoons of the olive oil. Spread the bread on a baking sheet and toast for 12 minutes, stirring once or twice, until golden and crisp.
In a large, ovenproof nonstick skillet, heat 2 tablespoons of the olive oil. Add the onion and cook over moderately high heat, stirring occasionally, until softened, about 5 minutes. Add the tomato and crushed red pepper. Season with salt and cook until the tomato is softened but not broken down, about 3 minutes. Add the bread and remaining 2 tablespoons of olive oil.
In a bowl, beat the egg whites with the milk and cheese and season with salt. Add the egg mixture to the skillet and cook over moderately high heat until the bottom is just beginning to set, about 3 minutes. Transfer the skillet to the upper third of the oven and bake for about 15 minutes, until the eggs are just set. Slide the frittata onto a plate, cut into wedges and serve right away.