Heat olive oil in a non stick pan. Add frozen Birds Eye Chopped Onions and cook for 2-3 minutes stirring continually. Stir in tomatoes and mushrooms and cook a further 1-2 minutes. Remove from pan and keep warm.
Wipe pan out with paper towel and spray with oil. Combine eggs, milk, salt and pepper and pour into pan. Cook omelette until set underneath. Place under a preheated grill and cook until the top is just set.
Place cooked omelette onto serving plate, top with onion mixture, grilled prosciutto and rocket leaves. Serve cut in half accompanied with toasted foccacia.