Preheat your oven to 190°C (375°F). Lightly coat the skillet with a teaspoon of olive oil to prevent sticking.
In a mixing bowl, whisk the egg whites with a pinch of salt and pepper until slightly frothy and light, about 30 seconds. Set aside.
Heat a tablespoon of olive oil in the skillet over medium heat. Add your chopped vegetables and sauté until tender and fragrant, about 3-4 minutes. You should see vibrant colors and a slight sizzle.
Pour the whipped egg whites over the cooked vegetables in the skillet, spreading them evenly with a spatula. Let cook gently over medium-low heat until the edges begin to set and turn golden, about 3-4 minutes. You’ll notice a slight bubbling and the mixture starting to firm up around the edges.
Sprinkle the feta cheese and chopped herbs evenly over the top of the egg whites. This adds flavorful contrast and visual appeal.
Transfer the skillet to the preheated oven and bake for 8-10 minutes, or until the frittata is puffed, set, and lightly golden on top. You may see it bubbling slightly and a firm texture in the center when gently shaken.
Remove the skillet from the oven and let it rest for 2-3 minutes. The residual heat will finish setting the eggs and help the edges crisp up.
Use a broad spatula to gently loosen the edges, then slice into wedges. Serve warm, garnished with extra herbs if desired, and enjoy the fluffy, golden perfection.