Reserve half cup corn; set aside. In a large saucepan cook chicken and onions until chicken is no longer pink. Add remaining corn with liquid, tomatoes, tomato sauce, chili powder, and salt. Heat to boiling; reduce heat. Meanwhile, to prepare dumplings, combine baking mix, cornmeal, milk, and reserved corn. Mix just until crumbly. Drop dough into 16 one ounce balls onto simmering chili. Cook, uncovered over low heat for 15 minutes. Cover and cook ten minutes more, or until dumplings are dry to the touch.