In a bowl, whisk together eggs, sugar, vanilla extract, milk, salt, lemon zest, and cinnamon.

Dip each croissant half into the egg mixture, coating well.

Heat oil in a pan over medium heat. Once hot, carefully fry croissant halves until golden brown on each side.

Remove with a slotted spoon and place on paper towels to drain excess oil.

Dust with powdered sugar or vanilla sugar and serve warm.