Melt butter in a large frying pan over low heat. Add onion, garlic and prosciutto. Sauté until onion is soft
Combine onion mixture, breadcrumbs, all cheese, lemon juice, oregano and season to taste
Using wet fingers loosen skin from chicken flesh to form a pocket and fill with cheese mixture. Combine potatoes, oil, sliced garlic and seasonings in a large roasting pan. Arrange chicken over potatoes and bake at 180˚C fan forced for 1 hour or until chicken is cooked and potatoes are golden
Serve chicken with roasted potatoes and steam vegetables