Preheat the oven to 350°F (175°C).
In a large mixing bowl, combine the shredded chicken, mixed vegetables, cooked rice, cream of chicken soup, milk, garlic powder, onion powder, black pepper, and salt. Stir until well combined.
Transfer the mixture into a greased 9x13 inch baking dish, spreading it evenly.
If using breadcrumbs, mix them with olive oil in a small bowl until coated. Sprinkle the breadcrumb mixture evenly over the casserole.
Top the casserole with shredded cheddar cheese.
Bake in the preheated oven for 25-30 minutes, or until the cheese is bubbly and golden brown.
Remove from the oven and let it cool for 5-10 minutes before serving.