Pound chicken with a meat mallet to flatten slightly (about 1/2 inch thickness).
Place 2-3 slices of the avocado onto each breast (You will have avocado left over I use this for my salad I serve on the side), remove tomatoes from oil and slice thinly ( 2 Tomatoes per breast) lay slices on top of avocado, finally top with sliced mozzarella. (quarter of cheese per breast). Fold breast over to cover, Wrap two slices of Prosciutto around each breast.
Pre-heat oven to 180c. Lightly oil an oven proof dish, place chicken breasts in dish and cook for 35-40 minutes or until cooked through.
Heat milk in a medium saucepan add chicken stock. Mix a little water with cornflour and add half the cornflour to milk. Stir until sauce thickens slightly.
Add the wine, Worcestershire sauce stir, whisk in mustard until blended.
Finally add the sugar, cream and remaining cornflour stir until sauce boils and thickens, add the parsley, stir and serve with chicken.
To serve: Place chicken on a plate, pour the sauce over and serve with salad on the side.