Grease a medium sized oven proof frypan or oven dish with oil. Place the baby spinach, spring onions, peas, courgette, feta and chicken in the dish. Season with salt and pepper and gently toss to combine.
Crack the eggs into a large mixing bowl and season well with salt & pepper. Whisk until combined and then pour over the vegetables.
Place in the oven to cook for 25 – 30 minutes until the frittata is golden and set in the centre.
Leave to sit for 5 minutes before slicing into wedges. Serve with relish or a side salad.