Cook the potatoes in a saucepan of boiling water for 8-12 minutes until tender. Drain and leave
to cool, then slice.
Heat the oil in an 18-20cm / 7-8 inches frying pan with a heatproof handle and cook the sliced
onion and red pepper until soft. Add the tomatoes and cook for a further minute.
Add the potatoes to the pan and spread out evenly. Beat the eggs, milk and cheese, and salt and
pepper to taste, in a bowl and pour over the potato mixture. Cook for 4-5 minutes until the eggs
are set underneath.
Meanwhile, preheat the grill to high. Place the frying pan under the grill and cook the omelette
for a further 3-4 minutes until the eggs are set.
Leave to cool, then cut into wedges and wrap in foil for a lunch box.