I made this dish last week for just the two of us and it was a "keeper" with leftovers for the next day.
In a shallow dish, like a pie plate, combine the flour, salt, pepper and oregano powder, mixing well so it blends completely. In a heavy skillet, heat the oil and butter until it bubbles slightly.
Completely coat the chicken breasts in the flour mixture and sauté in the bubbling oil/butter for at least two minutes or until the first side is slightly browned. Turn the chicken pieces to the other side. Add the mushrooms and onions around the edge of the pan. Brown the second side and pour the wine over the chicken. Cover and simmer for 10 minutes. You may want to turn the chicken again so it gets more brown on both sides.
Serve with jasmine rice or noodles or small potatoes and vegetable of your choice.