Add a tablespoon of oil to a skillet over a medium heat and add in the chopped onion. Cook until softened and starting to turn golden. Season with salt. Remove from the heat and set aside.
In a bowl mix together the cream cheese and one of the eggs. Add in the cooled onions, spinach, feta, chopped dill and lemon zest then season with salt and pepper.
Spray the cups of a muffin tin with cooking spray.
Roll out the puff pastry sheet to a 12 inch square then cut into 9 four inch squares.
Place each of the puff pastry squares into a muffin hole allowing the sides to hang over.
Add two tablespoons of the filling into each pastry square then bring the sides up to meet.
Place in the fridge to chill for a minimum of thirty minutes.
Beat the remaining egg with a tablespoon of water then brush the egg mixture over the pastry.
Bake in a preheated oven to 400ºF / 200ºC degrees for around 20 minutes until the pastry is puffed up and golden.
Delicious served both warm and cold.