Creating Chicken and Potato Casserole is straightforward when you follow these easy steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Sauté Ingredients: In a large skillet, heat olive oil over medium heat. Add chopped onions and garlic, cooking until the onions are translucent.
3. Add Chicken: Add the diced chicken to the skillet, seasoning with salt, pepper, and paprika. Cook until the chicken is browned on all sides.
4. Combine Ingredients: In a large bowl, mix together cream of chicken soup, milk, and shredded cheddar cheese until well combined. Stir in the diced potatoes and mixed vegetables if using.
5. Add Cooked Chicken: Incorporate the sautéed chicken mixture into the bowl, ensuring everything is evenly coated with the sauce.
6. Transfer to Baking Dish: Pour the entire mixture into a greased 9×13-inch baking dish, spreading it evenly.
7. Cover and Bake: Cover with aluminum foil and bake in the preheated oven for 30 minutes.
8. Uncover and Finish Baking: Remove the foil and continue baking for an additional 15-20 minutes or until the casserole is bubbly and the potatoes are tender.
9. Garnish: Once done, remove from the oven and sprinkle with fresh parsley for garnish, if desired.
10. Serve: Allow it to cool for a few minutes before serving, and enjoy this delightful one-pan wonder!