Spray 3 1/2- to 4-quart slow cooker with cooking spray. Place mushrooms and bell pepper in slow cooker.
Spray 12-inch skillet with cooking spray; heat over medium-high heat. Spray roast with cooking spray; add to skillet. Cook 3 minutes on each side or until browned. Place roast over vegetables in slow cooker.
In small bowl, stir ketchup, water, Worcestershire sauce, pepper and salt until blended. Pour over roast.
Cover; cook on Low heat setting 8 to 9 hours or until beef is very tender. Serve beef with vegetables and sauce and, if desired, hot cooked polenta. Garnish with parsley.