Cut chicken into thin slices and place in a wide, shallow bowl.
Sprinkle chicken slices generously with salt and pepper.
Sprinkle flour over chicken. Using 2 forks or your hands, toss the chicken so the slices are fairly evenly coated with flour.
Melt butter and oil in a large sauté pan on medium high heat.
Add chicken and sauté for 2-3 minutes per side until chicken is no longer pink.
Add mushrooms and sauté for another 2-4 minutes until most of the mushrooms are browned slightly. Pour sauce into the pan and bring to a boil. Cook for 2 minutes.
Taste and season with salt and pepper if needed.