Heat frypan over medium heat with olive oil, gently cook mushrooms and cherry tomatoes, set aside.
Lightly beat eggs with milk, salt and pepper and pour into pan. Stir until omelette starts to set and allow to cook evenly. When the underside is golden, lower heat and scatter with cooked mushrooms, tomatoes and cheese.
Cook for a further 30 seconds then slide the omelette from the pan onto a plate, folding over on itself. Sprinkle with chopped spring onion and serve.