Whisk the eggs in a bowl and add the oregano, mint and parsley. Season well.
Heat the oil in a large nonstick frying pan. Add the red onion and fry over a high heat for about 3-4 minutes or until brown around the edges.
Add the tomatoes, zucchini and olives and cook for 3-4 minutes or until the vegetables begin to soften.
Meanwhile, preheat the grill to medium-high.
Reduce the heat to medium and pour the eggs into the frying pan. Cook for 3-4 minutes, stirring as they begin to set, until they are firm but still slightly runny in places.
Scatter over the feta, then place the pan under the preheated grill for 4-5 minutes or until the omelette is puffed up and golden.
Cut into wedges and serve with a crisp green salad, if liked.