Preheat the oven to 350°F. Spray a medium (about 1 ½ - 2 quart) casserole dish with nonstick cooking spray. In the prepared dish, whisk together condensed soup and milk. If you like, this is a great time to add even more flavor with some extra herbs and spices (for instance, try ¼ teaspoon each of dried thyme, dried parsley, dried basil, garlic powder, and onion powder) or a splash of sherry.
Stir in the uncooked chicken, mushrooms, bell pepper, and pimentos. Season with salt and pepper, to taste.
Bake uncovered until the dish is hot and bubbly, the chicken is cooked through, and the vegetables are tender, about 40 to 45 minutes. Stir about halfway through to ensure even cooking. Taste and season with extra salt and pepper, if necessary. Garnish with fresh parsley.
Serve over hot biscuits, cooked rice, or pasta.