For the casserole: Preheat the oven to 375°F. Generously butter a 13-by-9-inch baking dish. In a small bowl, stir together the sour cream and onion ... the fried onions, potato chips, and parmesan.
Add chicken and rice and return to a simmer. Stir in peas, parsley, and sour cream; season with salt and pepper. Transfer the mixture to an 8-inch square baking dish. Top with breadcrumbs.