1. Preheat the oven to 200 °C (convection not recommended). Peel sweet potatoes and cut to 2 cm cubes. Wash zucchini and cut also into 2 cm cubes. Wash green onion and cut into 1 cm rings, chop parsley.
2. Mix eggs and milk. Add parmesan and a third of the parsley. Season with salt, pepper and nutmeg. Mix remaining parsley with lemon zest and chili flakes. Put aside.
3. Heat up oil in a non-stick, ovenproof pan. Cook sweet potatoes for 6 minutes at medium heat. Add zucchini and green onions and let them cook for 2 minutes. Season with some salt and pepper. Pour the egg-milk over the top and let it cook 1 minute until firm. Then bake the tortilla in the hot oven at the middle rack for 15-20 minutes.
4. Let the tortilla cool a little bit, take carefully out of the pan and cut into pieces. Spread the parsley mix on top and add ham if you want to. The tortilla tastes great cold or hot.
Preparation time: 45 minutes