Preheat the oven to 180°C, gas mark 4. Line 2-3 baking sheets with non-stick parchment.
Wilt the spinach in a colander over boiling water. Refresh under cold water and squeeze out the excess moisture with your hands. Roughly chop before placing in a bowl with the crumbled feta, breadcrumbs, lemon zest, chilli, dill and a generous seasoning of black pepper.
Unroll the filo on a lightly floured surface or board and cut the pile of 6 sheets into 2 lengthways so you have 12 long strips. Place a large tablespoon of the mixture at the bottom of a pastry strip and fold up diagonally to form a triangle. Place on the baking sheet, brush with the oil and sprinkle generously with zaatar. Repeat with the remaining filo strips until you have 12 borek.
Bake in the preheated oven for 20-25 minutes until golden and crisp. Remove and place on a rack to cool.
