Preheat the oven to 375°F (190°C). Lightly grease a 9×9-inch baking dish.
In a large skillet over medium heat, cook the ground beef and chopped onion until the beef is browned and the onion is soft, about 6-8 minutes. Drain excess fat.
Add chili powder, ground cumin, garlic powder, salt, and black pepper to the beef mixture. Stir well and cook for another 1-2 minutes. Remove from heat.
In a large mixing bowl, combine the Jiffy corn muffin mix, sour cream, milk, eggs, shredded cheddar cheese, drained corn, and diced green chilies. Mix until just combined.
Add the cooked ground beef mixture to the cornbread batter and stir until evenly incorporated.
Pour the mixture into the prepared baking dish and spread evenly.
Bake in the preheated oven for 35-40 minutes, or until the top is golden brown and a toothpick inserted in the center comes out clean.
Remove from the oven and let cool for 5 minutes before serving.