Heat oil in a large pan and saute onions until clear, then add the minced garlic and diced tomatoes. Cook until all the liquid is gone, then add the mushrooms and cook until all the liquid is gone. Add sherry, herbs and heavy cream and reduce by two-thirds. Adjust seasonings to taste.
Dredge chicken breasts in seasoned flour and saute until golden brown on both sides. Make sure that the chicken reaches at least 170 degrees before serving. This can easily be done by placing the chicken in the oven covered with a piece of parchment paper covered in butter or by using an old butter wrapper. This technique will help prevent the chicken from drying out. Keep your oven temperature at 275 degrees.
Once the sauce has reduced to the thickness desired, spoon on to a warm dinner plate and place two slices of chicken breast over the sauce. The plate has a lot of earth tone colors so I would recommend a mixture of julienne carrots and zucchini to add color. By pounding the chicken thin you will be amazed how many people think they are eating veal cutlets.