Preheat the oven to 200°C.
Peel & deseed the squash, then cut its flesh into thin slices. Place the slices onto a large baking sheet.
Mix the garlic with the oil and brush the squash slices with this. Bake for about 20 minutes until tender.
Meanwhile, mix the eggs and yogurt, then season with salt and pepper.
Grease and line a 20 cm square baking tray. Lay half of the squash in the tray, then pour over half of the egg mixture. Add the spinach, then cover with remaining pumpkin slices.
Pour the remaining egg over. Sprinkle with Parmesan cheese and bake for about 25 minutes until golden.
Cool the frittata in the tin for 5 to 10 minutes then cut it into squares or triangle shapes.