Preheat the oven to 200°C. Grease a 30 x 21cm baking dish with oil.
Gently heat the remaining oil in a large frying pan and cook the onion and garlic until tender. Add the spinach and cook until well wilted, drain off any excess liquid. Sprinkle over the dill and mint and mix through the feta. Season with salt and pepper remembering that the feta will also add saltiness.
In a bowl, whisk the eggs, milk, and ½ cup of the cheese. Arrange half of the bread in the base of a baking dish, top with the spinach mixture and sprinkle over the tasty cheese. Arrange the remaining bread over the top.
Evenly pour over the egg mixture and bake for 20 minutes until just set.