Preheat the oven to 350° F. Use nonstick cooking spray to grease a 9″x9″ baking dish or a 10-inch oven-safe pan.
Over medium-high heat, heat a large skillet. Add the ground beef and onion to the skillet. Cook, tossing frequently, until the ground beef is browned and no longer pink and the onion is softened. Remove any excess fat from the pan.
Add tomatoes, corn, olives, chilies, chili powder, garlic powder, and salt to the beef. Bring to a boil, then decrease the heat to low and continue to cook until the sauce has thickened, about 10 minutes. Fill the baking dish halfway with the beef mixture.
Combine the cornmeal, milk, sugar, and eggs in a medium mixing basin and stir just until incorporated. The mixture will be somewhat thin. Spread equally over the beef mixture in the pan, then sprinkle with cheese evenly.
Bake for 40-50 minutes, uncovered. The sauce should be boiling up the sides and the top should be golden brown.
Allow 5-10 minutes to rest before serving. If desired, top with sour cream and sliced green onions.
Garnish with chopped chives or parsley.