Use a 4-quart slow cooker. Place the rice into the bottom of the slow cooker insert and add the entire can of tomatoes with juice and the drained kidney beans. Top with taco seasoning and stir in water. Add stew meat.
Cover and cook on low for 8 hours, or on high for about 4 hours. Your casserole is finished when the rice has become bite tender – it’s okay if it breaks in half. Serve in wide-mouthed bowls with a spoonful of sour cream and a handful of shredded cheese, if desired.