Preheat the oven to 400 degrees.
Cut chicken breasts into small pieces (about 1 inch cubes) and place them in a greased 9×13 inch baking dish.
Top with frozen, mixed veggies.
Pour Campbell’s Oven Sauce over the chicken and veggies. Stir to coat.
Bake, uncovered, for 35 minutes at 400 degrees.
Remove the chicken pot pie casserole from the oven and spread three cups of warm mashed potatoes over the top.
Sprinkle with shredded cheddar cheese and French fried onions.
Bake for an additional 15 minutes, or until the chicken is fully cooked and the vegetables are tender.