Jalapeno Steak 'n' Mushrooms

Jalapeno Steak 'n' Mushrooms 2 1/2 pounds boneless beef chuck steak, cut 1 inch thick 1/4 cup packed brown sugar 1/4 cup reduced-sodium soy sauce 1/4 cup Worcestershire sauce 2 fresh jalapeno peppers, thinly sliced* 2 tablespoons red wine vinegar 1 tablespoon quick-cooking tapioca, crushed 4 garlic, thinly sliced 1 cup snipped fresh cilantro 2 3 1/2 inches diameter portobello mushrooms, stemmed, gills removed from caps, and caps cut into 1/2-inch-thick slices 1 medium onion, thinly sliced Fresh cilantro, chopped (optional) Hot cooked polenta, mashed potatoes, or mashed sweet potatoes (optional) Trim fat from meat. Cut meat into six serving-size pieces. Place pieces in a 3-1/2- or 4-quart slow cooker. In a medium bowl combine brown sugar, soy sauce, Worcestershire sauce, jalapeno peppers, vinegar, tapioca, and garlic. Stir in cilantro. Pour mixture over meat in cooker. Top with mushrooms and onion. Cover and cook on low-heat setting for 9 to 10 hours or on high-heat setting for 4-1/2 to 5 hours or until steaks are tender. If desired, sprinkle with cilantro just before serving. If desired, serve with hot cooked polenta.