Heat the olive oil in a large ovenproof frying pan over a medium-low heat. Toss in the red onion and cook for 5 minutes.
Meanwhile, crack the eggs into a large bowl. Add the milk, nutmeg, chopped mint and some salt and pepper and whisk well. Set aside.
Add the garlic to the pan and cook for 2 minutes, then toss in the zucchini and spinach and sauté until it begins to wilt. Pour the milk mixture into the pan, stir around for one minute, then remove from the heat.
Dot the goats cheese evenly over the surface of the frittata.
Place the fry pan in the oven for 20-25 minutes or until golden.
