Spray an 8 by 8 by 2-inch baking pan with nonstick spray. Drain all but 2 tablespoons liquid from Mexicorn. Place reserved 2 tablespoons liquid in a medium bowl. Add egg to liquid and whisk to blend. Stir in Mexicorn. Add corn muffin mix and stir until just combined. Transfer mixture to prepared pan. Bake until a toothpick inserted into center comes out clean, about 20 minutes.
Meanwhile, in a large resealable bag, toss turkey with flour until flour is absorbed into meat. Heat oil in a wide 2-quart pot over medium heat. Add turkey and cook until browned, about 5 minutes. Crush the canned tomatoes by hand and add tomatoes and liquid. Add beans and tomato paste. Simmer over medium-low heat until chili is slightly thick, about 8 minutes. Spoon chili into bowls. Top with sour cream, cilantro, and onion. Serve hot with corn bread.