Combine the stew meat, mushroom soup, mushrooms with their liquid, and onion soup mix in the crock of a slow cooker. Pour in red wine, if desired. Season with pepper.
Cook on Low for 8 to 10 hours, or on High for 4 to 6 hours.
In the last half hour of cooking time, bring the rice and water to a boil in a saucepan over high heat. Reduce heat to medium-low, cover, and simmer until the rice is tender, and the liquid has been absorbed, 20 to 25 minutes.