1. Coat a large nonstick skillet with cooking spray; place over medium-high heat. Sprinkle roast on all sides with pepper. Add roast to skillet, and cook until browned on all sides; place in a 3 1/2- to 4-quart electric slow cooker coated with cooking spray.
2. Combine 1 cup water and gravy mix; pour gravy over roast. Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours. Remove roast from sauce; cover roast, and keep warm.
3. Combine remaining 1/4 cup water and cornstarch, stirring until smooth. Slowly stir cornstarch mixture into gravy in slow cooker. Pour mixture into a 1-quart microwave-safe glass measure, stirring until blended. Microwave at HIGH 2 minutes or until thickened, stirring after 1 minute. Serve roast with gravy.