Preheat the Oven: Start by preheating your oven to 350°F (175°C) to get it ready for baking.
Mix the Base: In a large bowl, mix together the cooked rice or pasta, cream of mushroom soup, milk, garlic powder, onion powder, salt, and pepper. Stir until well combined.
Add Vegetables: Fold in the mixed vegetables, making sure they're evenly distributed throughout the mixture.
Cheese it Up: Add 1 1/2 cups of the shredded cheese to the mixture, reserving some for the topping, and mix it in well.
Prepare the Casserole Dish: Lightly grease a baking dish and pour the mixture in, spreading it out evenly.
Top with Cheese and Breadcrumbs: Sprinkle the remaining cheese on top, and if you're using breadcrumbs, add them for an extra crunch.
Bake: Place the casserole in the preheated oven and bake for about 30 minutes, or until the top is golden and bubbly.
Serve and Enjoy: Let the casserole cool for a few minutes before diving in. Enjoy with friends and family!