Preparation
In non stick skillet, heat oil.
Place chicken in skillet sprinkling both sides with ground pepper and cook until it loses its pink color, turning to brown both sides.
Remove chicken.
Reduce heat to medium, and add onion and mushrooms. Cook 4-5 minutes or until onions are tender.
Mix Soup with Mustard.
Add the Soup/mustard mixture to skillet with the browned onions and mushrooms.
Cook about 5 minutes, mixing throughly with a whisk or open slotted spoon.
Return Chicken to skillet with sauce and heat through.