Place chicken breasts into a plastic bag with flour, oregano, salt and pepper. Shake the bag so chicken breasts are completely covered in this mixture.
Pour olive oil in a large pan over medium high heat. Add chicken breasts and cook until browned and fully cooked inside, about 4-5 minutes on each side, or until internal temperature reaches 165 degrees F. Make sure to flip the chicken during this process to brown on all sides.
Pour beef broth and marsala wine over chicken in pan. Add mushrooms and onions to pan and stir.
Cover the skillet and simmer for 10 minutes. Flip the chicken half way to get all sides covered with gravy.
Serve next to mashed potatoes and vegetables! Enjoy!