Grease an ovenproof dish with a little oil using a pastry brush. Add the grated courgette, then scatter over the chopped bacon.
In a bowl, mix together the plain yoghurt, feta, parmesan and ground black pepper until well combined. Stir in the beaten egg until well combined.
Pour the egg-and-yoghurt mixture on top of the courgette and bacon mixture. Transfer the dish to the oven and bake for 20–25 minutes, or until the egg-and-yoghurt mixture has set and is golden-brown on top.
Remove the dish from the oven and set aside to cool slightly. Serve with the sliced tomatoes, if desired.