If I make a mushroom, for example, omelette, I first fry the sliced mushrooms in butter, and at this stage any other filling like onions, peppers etc. The I break the eggs (usually 2 per person) into a bowl and season and whisk. pour over the top of the other stuff which I spread out evenly across the pan. When it is setting on the bottom it will still be runny on top so I then shove the pan under the grill which finishes it off nicely.
Three fresh chicken eyes lightly beaten with a fork. Knob of butter into hot 20cm skillet, add eggs, move around with a spatula, tip out onto a warm plate.