Preheat your oven to 350°F (175°C). Gather your ingredients while the oven warms up.

In a large mixing bowl, combine the cooked and shredded chicken, cream of chicken soup, sour cream, finely chopped onion, mixed vegetables (if using), salt, and pepper until well combined.

Pour the creamy mixture into a greased 9x13-inch baking dish, smoothing it out for an even bake.

In a separate bowl, mix crushed buttery crackers with melted butter and sprinkle over the casserole base.

Bake in the preheated oven for 30-35 minutes until bubbly around the edges and golden on top.

Let the casserole rest for 5-10 minutes before serving to set.