Preheat oven to 400ºF. Warm vegetable oil in a skillet over medium heat. Add onion and garlic; cook, stirring, until softened, about 3 minutes. Add ground beef and cook, stirring to break up meat, until no longer pink, about 5 minutes. Stir in chili powder, tomatoes and 1/2 tsp. salt; cook mixture, stirring occasionally, until liquid is almost evaporated, another 5 minutes. Stir in beans and season to taste.
While chili is cooking, combine corn bread mix, egg, milk and cheese. Scrape chili into a 9-inch glass pie plate. Spread batter over chili. Bake until golden, 15 to 20 minutes. Let stand 5 minutes and serve.