Chop the onion and add to a large saute pan with the olive oil. Cook on a medium heat for 2 minutes, then add the chopped asparagus (you want it cut to pieces about an inch long).

Add the frozen peas and cook over the medium heat until they have warmed through - this should only take about 5 minutes.

Pour the egg mixture evenly over the veg in the pan, making sure it covers all of the vegetables, and move around quickly with a wooden spoon to ensure it fills any gaps. Cook over a low-medium heat (do not stir - or you get scrambled egg!) for 5-7 minutes until the egg has mostly set.

Crumble the feta evenly over the top and pop under a high grill until the egg is completely set and the top is golden brown (about 10 minutes).