Heat the oil in a large frying pan over a medium heat. Once hot, add the onion to the pan with a pinch of salt and cook until softened – about 5 minutes.
Slice 2 of the courgettes into coins about 2mm thick. Coarsely grate the last courgette.
Add the sliced courgettes to the pan on the heat and another pinch of salt then sauté on medium-low, until golden all over – about 15 minutes.
Stir in the garlic, grated courgette and frozen spinach with 60ml of water. Cover with a lid or large plate and leave on a low heat for the spinach to defrost (5-7 minutes). Remove the lid (careful of the steam!).
Spoon the contents of the pan to a 20cm pie tin (or oven proof frying pan) – you’re going to be baking the eggs in this.
Make 4 little wells in the mixture and crack the eggs into each well. Sprinkle with salt, black pepper and the grated parmesan.
Place under the grill in your oven until the whites are just set and the yolks are still slightly runny – 3-5 minutes. Remove from the oven and crumble over the feta cheese. Sprinkle on more black pepper and the basil leaves. Serve immediately with toasted bread for dipping.