Preheat the oven to 350°F and coat a 9×9-inch (or 2½-quart) baking dish with nonstick spray. In a medium bowl stir together the cornbread mix, milk and egg until just combined, then spread the batter evenly in the prepared dish. Bake until the top looks set and lightly golden, about fifteen minutes, then remove from the oven.

While the cornbread bakes, brown the ground beef in a skillet over medium heat, breaking it into crumbles and cooking until no pink remains. Drain off any excess grease, then stir in the taco seasoning, water, drained Mexicorn and drained Rotel. Simmer for two to three minutes until the flavors meld and the mixture is slightly thickened.

Spoon the beef and vegetable layer over the baked cornbread, spreading it into an even layer. In a clean bowl combine the sour cream with one cup of the shredded cheese blend and the chopped green onions, stirring until smooth. Gently dollop and spread this creamy mixture over the beef layer, taking care not to mix the layers.

Sprinkle the remaining cup of shredded cheese evenly over the top. Return the dish to the oven and bake uncovered until hot and the cheese is melted, about twenty-five minutes. Let the bake rest for five minutes before slicing.

Serve warm with optional toppings such as shredded lettuce, sliced olives, diced tomatoes or a drizzle of taco sauce.