Step 1: Prepare all the necessary ingredients before starting.
Step 2: Combine the flour, salt, black pepper, and oregano in a shallow dish or bowl to create the coating for the chicken.
Step 3: Thoroughly coat each chicken breast in the seasoned flour mixture, ensuring an even layer.
Step 4: Heat the butter and olive oil in a large skillet over medium heat. Once hot, add the coated chicken breasts and cook until they are golden brown on each side.
Step 5: Flip the chicken breasts over, add the mushrooms around them, and then pour the Marsala wine and cooking sherry over the top.
Step 6: Cover the skillet and let the chicken simmer for about 10 minutes, turning the chicken once halfway through, until it is thoroughly cooked and the juices run clear.
Step 7: Serve the Chicken Marsala hot, spooning some of the mushrooms and sauce over the top of each breast.