Finely chop the red onion, chop the tomato into large chunks and thinly slice the mushrooms.
In a non-stick frying pan, melt 1 tsp of butter on a low heat.
Cook the onion, tomato and mushrooms for 2 minutes, and set aside.
Finely chop the parsley and stir together with the cooked vegetables.
Add the remaining 1 tsp butter in the pan and melt.
Meanwhile, gently whisk the eggs, milk, salt and pepper together in a bowl using a metal fork.
Pour the egg mix into the pan and leave to cook on a low heat until cooked through.
Add the cooked veg on top of the omelette in the pan with the chopped parsley and chives, fold over, leave to warm thorough for 2 minutes and serve.