Preheat the oven to 350°F (175°C). Preheating ensures even baking and prevents the casserole from cooking unevenly.
Begin by browning the ground beef in a large skillet over medium-high heat. Use a spoon or spatula to break up the ground beef as it cooks, ensuring it's evenly browned throughout.
Add the drained corn, kidney beans, salsa, taco seasoning, water, salt, pepper, and garlic powder to the skillet. Stir well to ensure all ingredients are evenly distributed.
Pour the ground beef mixture into a 9×13 inch baking dish that has been sprayed with nonstick spray. This prevents sticking and makes serving easier.
Top the ground beef mixture with shredded cheese ensuring it's evenly distributed across the surface for maximum meltiness.
In a medium bowl, combine the corn muffin mix, creamed corn, milk, and sour cream until just combined to avoid overmixing which can lead to a tough texture.