Preheat oven to 375°F. Grease the baking dish.
Heat oil in skillet. Add onion, cook until soft.
Add ground beef. Cook until browned. Drain fat.
Stir in taco seasoning, salsa, corn, and beans.
Simmer for 5 minutes. Remove from heat.
Pour meat mixture into prepared baking dish.
Sprinkle shredded cheese evenly over meat layer.
In a bowl, mix cornbread, milk, egg, sour cream.
Pour cornbread batter on top of meat mixture.
Spread gently to cover evenly. Bake for 30 minutes.