Preheat the oven to 375°F (190°C). Grease a 9×9-inch baking dish with vegetable oil.
In a large skillet, heat 2 tablespoons of vegetable oil over medium heat. Add the diced onion and green bell pepper and sauté for 3-4 minutes until softened.
Add the ground beef to the skillet with the vegetables. Cook, breaking it apart with a spoon, until the beef is fully browned and cooked through, about 6-8 minutes. Drain excess fat if necessary.
Stir in the ground cumin, chili powder, garlic powder, salt, and black pepper. Mix well and cook for another 1-2 minutes. Remove from heat and set aside.
In a large mixing bowl, combine the Jiffy corn muffin mix, milk, and egg. Stir until just combined.
Fold in the canned corn, diced green chilies, shredded cheddar cheese, shredded Monterey Jack cheese, and chopped cilantro.
Add the cooked ground beef mixture to the batter and gently fold until evenly combined.
Pour the mixture into the prepared baking dish and spread it out evenly.
Bake in the preheated oven for 40-45 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.