Preheat oven to 350°F (175°C).

Thaw and drain the frozen mixed vegetables.

In a large bowl, combine the thawed vegetables, cream of mushroom (or celery) soup, half of the shredded Swiss cheese, sour cream, black pepper to taste, and half of the French fried onions.

Mix well to combine all ingredients.

Pour the mixture into a shallow one-quart casserole dish.

Cover the casserole dish with a lid or aluminum foil.

Bake in the preheated oven for 30 minutes, or until the vegetables are tender.

Remove the casserole from the oven.

Sprinkle the remaining Swiss cheese and French fried onions in diagonal rows across the top of the casserole.

Return the casserole to the oven, uncovered.

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

Remove from oven and let cool slightly before serving.