Brown short ribs in large nonstick skillet over medium-high heat. Remove and place in slow cooker. Add onion, carrots, garlic and thyme.
Drain fat from skillet. Add 1 cup water and Knorr® Classic Brown gravy mix, stirring well and scraping brown bits from bottom of skillet. Pour over short ribs.
Cover and cook at LOW 8 hours or until short ribs are tender. Remove short ribs and vegetables to serving platter; cover to keep warm.
If desired, remove excess fat from slow cooker. Thicken gravy by stirring flour with remaining 2 tablespoons water in small bowl. Add to slow cooker and cook at HIGH until thickened, about 5 minutes. Serve with short ribs and vegetables.