For the feta and spinach croissants with filo dough, fill a pot with 1 cm of water and bring to a boil. Wash the spinach and cook in the boiling water for 1-2 minutes until it has collapsed. Remove, drain and squeeze well with your hands. Then finely chop the spinach and mix it with the spring onions, eggs, parsley and dill in a large bowl. Finely crumble the feta and add it and mix everything well. Season to taste with pepper and salt.
Preheat the oven to 190 degrees. Coat the filo pastry sheets individually with oil and cut in half lengthwise. Spoon some filling onto the end of the pastry sheet (making sure to leave the edges free) and loosely roll up and bend into croissants.
Place the feta and spinach croissants with filo pastry on a baking tray with baking paper and bake in the oven for about 25 minutes until golden brown.