Preheat oven to 350°F and grease a 9x13 inch baking dish.
In a large bowl, mix together chicken, rice or pasta, soup, sour cream, cheese, peas, carrots, and seasonings.
Spread mixture evenly into the baking dish.
If topping with breadcrumbs, mix breadcrumbs with melted butter and sprinkle over the casserole.
Bake uncovered for 30–35 minutes, until bubbly and golden on top.
Let rest for 5 minutes before serving.