Toss together 1/2 cup of the cheddar cheese and the cornstarch; set aside.
Place chicken, broccoli, onion, broth, 1/4 teaspoon each salt and pepper and the cheddar cornstarch mixture into slow cooker. Cover and cook on HIGH for 3 hours or on LOW for 4 hours.
Remove lid and stir remaining 1/2 cup cheddar cheese and 1/4 teaspoon each salt and pepper into slow cooker. Sprinkle crushed crackers over top and serve immediately with rice, if desired.
