Set your oven to 375°F (190°C) to preheat. Dice 1 pound of chicken breast into bite-sized pieces and trim 2 cups of fresh green beans, cutting off the ends. Having everything prepped ahead makes the assembly quick and easy.
In a large mixing bowl, combine 1 cup of cream of chicken soup with 1/2 cup of sour cream. Stir in 1 teaspoon garlic powder, 1 teaspoon onion powder, 1/2 teaspoon salt, and 1/4 teaspoon black pepper until well blended. This mixture will be the rich, flavorful binder for the chicken and green beans.
Add the diced chicken and trimmed green beans into the bowl with the creamy sauce. Toss everything together until the chicken and beans are evenly coated in the sauce.
Pour the mixture into your prepared baking dish and spread it out evenly. Sprinkle 1 cup of shredded cheddar cheese over the top, distributing it to cover the entire surface layer. This cheese will melt and create a savory blanket over the casserole.
In a small bowl, toss 1 cup of breadcrumbs with 2 tablespoons of olive oil until the crumbs are lightly coated. This helps the topping crisp up nicely. Sprinkle the breadcrumb mixture evenly over the cheese layer.
Place the baking dish in the preheated oven and bake for 30-35 minutes. The casserole should be bubbly around the edges, and the breadcrumb topping golden brown. This baking time ensures the chicken is fully cooked and the green beans are tender yet crisp.
Remove the dish from the oven and let it rest for 5 minutes before serving. This brief resting period allows the casserole to set slightly, making it easier to scoop onto plates.