1Spray 12-inch nonstick skillet with cooking spray. If beef roast comes in netting or is tied, do not remove. Sprinkle beef with salt and garlic. Place beef in skillet; cook over medium-high heat 5 to 6 minutes, turning occasionally, until brown on all sides.
2Spray 4- to 5-quart slow cooker with cooking spray. Place mushrooms in cooker. Place beef on mushrooms. Spread tomatoes over beef. Pour dressing over mixture in cooker.
3Cover; cook on Low heat setting 9 to 11 hours.
4Remove beef from cooker; place on cutting board. Remove netting or strings; slice beef. Serve mushrooms and juices with beef.