Peel and finely chop the shallot. Wash the tomatoes, halve and remove the seeds. Wash the parsley, shake dry and chop the leaves.
Cut the chicken breast fillets horizontally into 2 thin slices.
Beat the slices between two layers of cling film with a heavy pan or a meat tenderizer until an even thickness. Season with salt and black pepper.
Heat a dry pan and fry the tomato halves, cut side down, over a high heat until browned then remove from the pan.
Pour the oil into the pan and fry the chicken pieces for 1 minute on each side, then remove from the pan. Add the shallots and tomatoes to the pan and cook for 1 minute.
Add the Marsala, then the stock and simmer for 2-3 minutes.
Briefly heat the chicken pieces with the parsley in the pan and season with salt and pepper. Serve with brown rice or wholewheat pasta.