Wash the zucchini blossoms and carefully remove their stems.
In a small mixing bowl combine feta cheese, Greek yogurt, egg yolk and mint leaves. Season with a tiny bit of salt and ground pepper.
Stuff each zucchini blossom with a teaspoon of filling and gently twist the petals to seal.
In a very small bowl whisk together the egg white along with 2 tablespoons of water. Set aside. Add some flour in another mixing bowl and set aside.
Fill a frying pan about ⅔ with oil. Heat over medium-high heat.
Dip each zucchini blossom first into the egg mixture and then coat with flour.
Add half the zucchini blossoms into the pan (making sure they're not overcrowded) and fry for approximately 2 minutes on each side.
Transfer the blossoms on paper towels to drain any excess oil before serving.