Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package instructions until al dente (usually 7-8 minutes). Drain and set aside.
If you haven’t cooked your chicken breast yet, poach or bake it until fully cooked, then shred it with two forks. Toss the shredded chicken with the taco seasoning, garlic powder, onion powder, salt, and pepper to ensure every bite is flavorful.
In a large skillet, heat olive oil over medium heat. Add the seasoned chicken, black beans, diced tomatoes with green chilies, and corn kernels. Stir everything together and cook for 3-5 minutes until heated through and fragrant.
In a mixing bowl, combine sour cream, salsa, shredded cheddar, and Monterey Jack cheeses. Stir until smooth and creamy. This mixture will bind all the ingredients and add a rich, tangy flavor.
Preheat your oven to 350°F (175°C). In your casserole dish, combine the cooked macaroni and the chicken-veggie mixture. Pour the creamy cheese sauce over the top and stir gently to coat everything evenly.
Bake uncovered for 20-25 minutes, or until the cheese is melted, bubbly, and slightly golden on top. For an extra layer of flavor, you can broil for the last 2-3 minutes—just keep a close eye to avoid burning.
Remove the casserole from the oven and let it rest for 5 minutes before serving. Sprinkle chopped green onions on top for a fresh, crisp finish. Serve with extra salsa and sour cream on the side if desired.