Saute spinach with olive oil in a skillet over medium heat until spinach is wilted. Remove from heat and combine in a bowl with feta, parmesan, green onions, garlic powder, red pepper flake, pepper, and 1 egg.
Slice each sheet of puff pastry into nine squares. Spoon feta mixture into center of each square, leaving space for folding. Fold pastry diagonally.
Whisk remaining egg with 1 tablespoon of water. Brush egg wash over top of pastries.
Bake for 25 minutes.
Recipe by Rachel Schultz at https://rachelschultz.com/2018/01/05/feta-spinach-mini-pastries/