Start by bringing a large pot of salted water to a boil. Add the 8 oz of elbow macaroni and cook according to package instructions until al dente. Drain the pasta and set it aside.
In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the diced chicken breast and cook until it’s no longer pink, about 5-7 minutes. Remove the chicken and set aside. In the same skillet, add the chopped onion and minced garlic, sautéing until soft and fragrant, about 3-4 minutes.
Return the chicken to the skillet. Sprinkle the taco seasoning over the mixture and stir well to coat the chicken and onions evenly. Pour in the diced tomatoes with green chilies, black beans, and corn. Stir to combine and let everything simmer gently for 5 minutes, allowing the flavors to meld together.
In a large bowl or directly in the baking dish, combine the cooked elbow macaroni with the chicken mixture. Add the sour cream, half of the shredded cheddar, and half of the Monterey Jack cheese. Stir until everything is evenly coated and creamy.
Transfer the pasta mixture into a greased baking dish. Sprinkle the remaining cheddar and Monterey Jack cheese evenly on top. Bake in a preheated oven at 350°F (175°C) for 20-25 minutes, or until the cheese is melted and bubbly and the casserole is heated through.
Once out of the oven, sprinkle the chopped cilantro over the casserole for a fresh burst of flavor. Serve hot, paired with a side salad or your favorite Mexican-inspired sides.