Preheat the oven to 375°F (190°C). Grease a 9×9 inch baking dish with vegetable oil or cooking spray.
In a large skillet over medium-high heat, add the ground beef. Cook until browned and fully cooked, breaking it apart with a spatula, about 6-8 minutes.
Drain excess fat from the skillet. Stir in taco seasoning mix, water, ground cumin, garlic powder, and salt to taste. Simmer for 3-4 minutes until the sauce thickens slightly. Remove from heat.
In a large mixing bowl, combine the Jiffy corn muffin mix, eggs, milk, and sour cream. Stir until just combined.
Add the canned whole kernel corn, cream-style corn, chopped green onions, and half of the shredded cheddar and Monterey Jack cheeses to the batter. Mix gently.
Fold the cooked ground beef mixture into the cornbread batter until evenly distributed.
Pour the mixture into the prepared baking dish and spread evenly.
Sprinkle the remaining shredded cheddar and Monterey Jack cheeses evenly over the top.
Bake in the preheated oven for 35-40 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
Remove from the oven and let the casserole cool for 5 minutes before serving.
Garnish with fresh cilantro leaves if desired and serve warm.