Preheat the oven to 180°C (350°F). Cut the sun-dried tomatoes into thin strips. Clean the mushrooms and slice them thinly. Halve the leeks lengthwise, wash them thoroughly, and cut them into thin strips. Squeeze the excess water from the thawed spinach over the sink with your hands, then tear the leaves apart.

Pour oil into a small bowl, dip a brush in it, and grease a casserole dish or frying pan with a little oil. Line the pan with the filo sheets, brushing each layer with a little oil.

Crack the eggs into a large mixing bowl and whisk them together with the cottage cheese and harissa. Gently fold in the tomatoes, chopped vegetables, spinach, and about two-thirds of the cheese. Season with salt and pepper.

Pour the egg mixture into the filo-lined dish, distribute the remaining cheese over it. Roll up the overlapping edges of the filo and fold them inwards, brush with the remaining oil.

Bake the quiche for one hour at 180°C (350°F) using conventional oven settings (top and bottom heat). The quiche is done when the egg mixture is completely set and has a crispy, golden-brown surface.