In a non-stick frying pan, heat the olive oil and fry the onions until very soft.
Meanwhile, preheat the grill to medium.
When the onions are translucent, add the spinach gradually until it has wilted down and stir well to combine.
In a large bowl whisk the eggs with a generous amount of salt and pepper.
Top the spinach mixture with small chunks of the goat’s cheese.
Preheat the oven to 180°C / 350°F / Gas mark 4.
Line a small roasting tin with greaseproof paper.
Pour in the eggs, making sure the mixture covers the tray evenly.
Cook until the sides have started to set,about 15-20 minutes.
Transfer the tray to the grill and let the frittata set, go golden and puff up slightly.
Shake the tray gently to check it has set. If it still looks runny, return it to the grill for a few more minutes.
Remove from the grill and use a palette knife to release the sides.
Slide the frittata onto a plate or board and serve sliced wedges.