Preheat oven to 350°F (175°C).

Place the thawed and drained mixed vegetables in a casserole dish.

In a separate bowl, combine the cream of mushroom soup, half of the shredded Swiss cheese (1/2 cup), sour cream, salt, and pepper.

Add half of the can of French fried onions to the soup mixture.

Pour the soup mixture evenly over the vegetables in the casserole dish.

Cover the casserole dish with a lid or aluminum foil.

Bake in the preheated oven for 30 minutes.

Remove the cover and top with the remaining Swiss cheese and French fried onions.

Bake uncovered for an additional 5 minutes, or until the cheese is melted and bubbly and the onions are golden brown.

Let cool slightly before serving.