Start by chopping the bell peppers and spinach into small, even pieces. Set aside.
In a bowl, whisk the egg whites until they become frothy and light, about 30 seconds. Add a pinch of salt and pepper to season.
Heat the olive oil in your skillet over medium heat until it shimmers and smells slightly nutty.
Add the chopped bell peppers to the skillet and sauté for 2-3 minutes until they soften slightly and release a fresh aroma.
Stir in the chopped spinach and cook for another minute until wilted and vibrant in color.
Pour the whipped egg whites evenly over the sautéed vegetables, tilting the skillet slightly to distribute them smoothly.
Let the egg whites cook undisturbed on the stove for 2 minutes until the edges start to set and become slightly opaque.
Sprinkle the crumbled feta cheese and chopped herbs over the top, distributing evenly for flavor and visual appeal.
Transfer the skillet to a preheated oven at 180°C (350°F) and bake for 8-10 minutes until the top is puffed, golden, and the center is just set, with a slight jiggle.
Remove the skillet from the oven using oven mitts and let it rest for 2 minutes to settle and finish cooking gently.
Slice the fluffy frittata into wedges and serve warm, garnished with additional herbs if desired. Enjoy the light, tender texture and vibrant flavors!
