Mix the butter in a bowl with half the garlic. Get everything in bowls or on plates ready to take outside. Light the barbie.
Heat a sturdy roasting tin on the barbie rack, in the oil to coat the tin’s base. Lay in the prosciutto and crisp on both sides. Set it aside.
Season the chicken and brown on both sides in the tin. Stir in the rest of the chopped garlic, and add the chopped tomatoes, stock and oregano. Simmer for 3 minutes, turn the breasts over and simmer for a further 3 minutes.
Tip in the cannellini beans, turn the chicken over and simmer for another 3 minutes, then turn again and simmer for 3 minutes more. Now taste the sauce and add a little seasoning if you think it’s needed.
Towards the end of the chicken’s cooking, toast the ciabatta on both sides on the barbie – you may need to do this in batches, depending on the size of your barbie.
Toss the tomatoes and chopped basil into the chicken mix. Let the tomatoes soften slightly, then top with the crisp prosciutto and scatter over the whole basil leaves. Spread the garlic butter on the ciabatta and arrange butter-side up around the edge of the chicken, or put the bowl of garlic butter on the table for guests to spread their own. Serve hot, with mixed leaf salad.