Set the oven to 190c and brush a 1.5 litre dish liberally with the oil.
Cook the potatoes in boiling salted water so it is just cooked. Run under cold water to help cool, then slice and spread in the dish. Alternatively, used leftover, or tinned potatoes.
Add the drained tuna, flaked into chunks, green beans, tomatoes, olives, red onion and pepper.
Beat together the eggs and milk then pour over the vegetables.
Bake for 30- 40 mins until set (if your dish is small but deep, the cooking time will be slightly longer).
If you wish to cook this in a pan, brush the pan with oil, turn to a medium heat then add the vegetables, tuna then the egg mixture. Stir a little at first to partially cook then cover and cook for about 20 mins finishing under the grill to brown. If you have no lid, just fashion a ‘lid’ with tin foil.