POUND chicken breasts between sheets of plastic wrap until about 1/4-inch thickness.
COMBINE flour, salt, pepper and oregano in a mixing bowl. Dredge chicken pieces in the flour, shaking off any excess.
HEAT oil and butter in a skillet over medium heat. Cook chicken breast on medium heat for about 2 minutes on the first side, until lightly browned. Turn breasts over to cook the other side, then add mushrooms. Add Marsala wine around chicken pieces (CAUTION: a small flame will appear upon adding).