Break the eggs into a bowl, add the yogurt and parmesan cheese and beat together well, then season with salt and pepper.
Gently heat the oil in a cast-iron skillet or frying pan
Add the onion and courgette and sauté for about 5 minutes until soft.
Add the spinach and cook down for a further 2 minutes.
Stir in the tomatoes and heat for a further 2 minutes and then remove from the heat.
Pour the egg mixture into the pan and distribute it around to cover all the vegetables.
Arrange the sliced tomatoes around the pan.
Place the skillet in the oven and bake the frittata until golden for about 15 to 20 minutes.
Notes
Serve hot or at room temperature. The frittata will keep for 2 - 3 days in the refrigerator.To add some carbs to this recipe I added some slices of focaccia from my focaccia recipe but they are not included in the nutrition label.