Mix the vegetables with the flour, egg yolk, green herbs and most of the feta cheese, gently mashing them together with a fork. Season with salt and pepper.
Whisk the egg white into a light foam, then gently fold into the vegetable mixture.
Pour oil into a pan (oils should be about 1 cm deep) or use a deep-fryer and heat. When the oil is hot, add dollops of the batter and press them down slightly with the back of the spoon.
Cook the fritters for 3-4 minutes on both sides until golden, then transfer them to a plate lined with paper kitchen towel.
Repeat with the remaining batter.
Serve warm with a side salad, or at room temperature as nibbles.