Heat grill to high. Whisk the eggs together in a large bowl, add the baking powder and turmeric, then season with salt and pepper. Stir in most of the herbs, then add the spring onions, currants and walnuts.

Drizzle the oil into a small ovenproof, non-stick frying pan over a medium heat. Pour in the herby egg mixture and cook for 8-10 mins until the egg is nearly set, then put the frittata under the grill for a final minute until cooked through. Sprinkle over the remaining herbs and the crumbled feta to serve.