Preheat oven to 350°F.
Mix together the melted butter, sugar, egg, Greek yogurt, lemon zest, lemon juice, salt, vanilla, and flour until combined.
Pour the batter into a prepared baking pan.
Bake for 20–22 minutes at 350°F.
Let cool for 30 minutes.
Whisk together the powdered sugar and lemon juice until smooth.
Spread over the cooled blondies, let the glaze set, then slice and enjoy.