Heat oil in a skillet over medium-high heat. Season chicken with salt and pepper, then add to hot oil and cook until browned, 3 to 5 minutes. Stir in onion and mushrooms; continue cooking until onion is translucent, 5 to 7 minutes.
Pour condensed soup and Marsala wine over chicken mixture; cook until hot and chicken is no longer pink in the middle, 3 to 5 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).
