Thaw the frozen spinach and filo pastry sheets to room temp.
Finely dice the white onion. Add to a bowl.
Once spinach is at room temp, place it onto some cheesecloth. Squeeze out all the excess liquid then add to the bowl with the onions along with the feta, egg, parsley, lemon rind and a lot of cracked black pepper. Stir to combine.
Lightly grease a muffin tin tray with the olive oil.
Cut the filo pastry in half lengthways then half again from top to bottom. You should have four sections.
Place one square in a muffin case. Brush with a little oil then place another filo square on top. Brush with oil again. Repeat until all muffin cases are filled
Then place a spoonful of the spinach mixture in the centre. Fold the sides of the filo around the top, brush again with oil, grate some lemon rind on top, add a scrunch of black pepper and cook in the oven for 30-35 min.
Once the top is nice and golden, remove from oven and let cool slightly.