Mince the garlic. Chop the zucchini in cubes. Chop the tomato in cubes.
Zest the lemon. Roughly chop the mint leaves. Crumble the feta cheese.
Put the oil in a large frying pan. Add the zucchini cubes, garlic, and the salt. Sauté for 4 minutes, stirring often.
Add the spinach and lemon zest. Sauté for 3 minutes.
Add the tomato chunks and chopped mint. Cook for 1 further minute, stirring carefully.
Leave to cool for at least 10 minutes.
Oil a quiche dish and place a round of baking paper on the bottom of it.
Layer the sheets of filo pastry one on top of the other in the quiche dish.
In a medium-size bowl, whisk the eggs and yogurt together. Sprinkle with 1/2 tsp salt.
Add the cooked vegetables to the pie and spread them out over the filo pastry.
Sprinkle the crumbled feta over the top.
Pour the egg mixture over the other ingredients.
Bake at 180 degrees C (350 degrees F) for 40 - 45 minutes, until the custard is set.