Heat 2 tablespoons of the oil in a large skillet over medium-high. Add the turkey and onions; cook, stirring to crumble the turkey, until browned, about 7 minutes. Add the garlic, chili powder, and 1 teaspoon of the salt, and cook, stirring often, until fragrant, about 1 minute. Transfer to a 5- to 6-quart slow cooker coated with cooking spray. Stir in the tomatoes, stock, and beans until blended.
Whisk together the flour, cornmeal, baking powder, and remaining ½ teaspoon salt in a large bowl until well blended. Stir in the egg, milk, cheese, and remaining 4 tablespoons canola oil. Pour the cornmeal batter over the turkey mixture in the slow cooker, gently spreading to cover completely. Cover and cook on LOW until the chili is hot and the crust is lightly browned and cooked through, about 4 hours and 30 minutes. Sprinkle each serving with the cilantro leaves, if desired.