Heat oven to 190°C/170°C fan/gas 5.
Heat 1 tsp olive oil in a pan on a medium heat.
Add the spring onion and cook for 3 minutes.
Add the spinach and cook until it just wilts.
Stir in the turmeric and cook for another 2 minutes. Transfer from the heat.
In a large bowl, whisk the eggs with the yogurt, herbs, spring onions and spinach; season.
Heat 2 tsp olive oil in the same pan on a medium heat. (A 20cm pan is ideal for 2 servings).
Once hot, wipe the oil around the pan with kitchen paper to spread it evenly.
Pour in the frittata mix and turn the heat to low.
Sprinkle the walnuts on top.
With a spatula, draw the edges into the middle a couple of times.
Cook until it is beginning to set around the edges, around 5 minutes.
Crumble the feta on top and finish cooking in the oven until it is fully set, but still moist in the center, around 8-10 minutes.
Transfer from the oven, leave to cool for a few minutes then gently slide onto a chopping board.
Slice into 6 wedges. Serve with mixed green leaves.
Experiment with different herbs - try adding dried sumac and oregano instead of the parsley and coriander.