Preheat the oven to 400°F. In a large skillet over medium-high heat, brown the ground beef, bell pepper, and onion until the meat is no longer pink. Drain off the excess grease.
Return the meat mixture to the skillet. Stir in the taco seasoning, green chiles, and water. Bring to a simmer, and then reduce the heat and simmer gently until the sauce thickens, stirring frequently, about 3-5 more minutes. Add the corn and shredded cheese during the final 1-2 minutes of cooking.
Spoon the beef mixture into a 9-inch deep-dish pie plate (or other 2-quart baking dish) that has been sprayed with nonstick cooking spray. Let the mixture cool slightly while you prepare the topping.
In a medium bowl, combine the corn muffin mix, egg, and milk; mix well.
Spread the batter on top of the filling.
Bake until the top is golden brown and a toothpick inserted in the center of the cornbread crust comes out clean, about 22-24 minutes. If the topping starts to brown too quickly before it has cooked through, just cover the top lightly with foil and continue baking.
Let stand for about 5 minutes before serving. Garnish with your favorite taco toppings.
Video
Notes
Some readers have found that the cornbread topping sinks into the filling a bit. I haven't noticed this issue; however, if you'd like to avoid this, just let the filling cool before spreading the cornbread mixture on top.