Bring a large pan of water to the boil and add the potatoes. Simmer for 5-6 minutes until just tender. Drain well and set aside.
Meanwhile, heat the olive oil in an ovenproof 26cm frying pan. Add the red onion, pepper, courgette and herbs, and cook for 8-10 minutes until golden brown, stirring occasionally. Add the garlic and cook for another minute.
Whisk the eggs together with the milk, parmesan, parsley and some seasoning. Stir the olives and cooked potatoes through the veg, then pour over the egg mixture.
Cook for 12-15 minutes until almost set, and golden brown underneath. To finish, put the pan under a preheated grill for 4-5 minutes until golden brown on top.
Serve sliced into wedges alongside the salad.