In 10-inch skillet, heat oil over medium-high heat. Sprinkle beef with salt and pepper; place in skillet. Cook 4 to 6 minutes, turning once, until well browned.
Meanwhile, spray 3- to 4-quart slow cooker with cooking spray. In cooker, mix onion, carrot and mushrooms.
Cut browned beef into 4 pieces; place in cooker over vegetables. In same skillet, mix soup and tomato sauce. Pour over beef.
Cover; cook on Low heat setting 8 to 10 hours. Stir sauce well before serving over beef.