Thaw the spinach, then drain it in a sieve and squeeze out most of the moisture with your hands
Dice the onion finely
Add 2 tbsp olive oil to a medium heat pan and sautee the onions until soft and starting to color, 10 minutes
Add the onion mixture to a bowl with the cold, drained spinach. Add the salt, pepper, parsley, sumac, lemon juice, and shatta chili paste. Mix thoroughly.
Add the feta crumbles and beaten egg and mix again.
Cut each pita in half and carefully open to reveal the pocket. Cut in half again to create 12 open wedges.
Fill each wedge with a half-inch or so layer of the spinach mixture, squeezing to spread evenly and patting into the edges with fingers to avoid filling spilling.
Brush each pita wedge with olive oil, top and bottom.
Bake at 350° F for 20 minutes, flipping each wedge once halfway through. Serve hot.
Notes
I used dried parsley because that's what I had on hand, but if you want to replace it with a handful of fresh parsley finely chopped, please do! It will likely be an improvement, but this is pretty great as is!