Cut the tomatoes in half.
Heat 1 Tbsp of olive oil in a frying pan, add the tomatoes and cook for 2-3 minutes (and the dried oregano, if used).
Meanwhile, whisk the eggs with a couple of pinches of salt in a bowl. Pour this onto the tomatoes, letting it spread out evenly - try to move the tomatoes to one side, it will be easier to fold the omelette later. Add the fresh oregano (if that’s used).
When the egg is half set, crumble the feta on top.
Put a lid on and cook for about 5 minutes.
When the omelette is set, fold it over and rest for a minute or so to allow the cheese to melt.
Slide it onto a plate, cut in half and serve.