1Trim excess fat from beef. Spray 12-inch skillet with cooking spray; heat over medium-high heat. Cook beef in skillet about 5 minutes, turning once, until brown.
2Place beef in 4- to 5-quart slow cooker. Pour dressing over beef. Cover and cook on low heat setting 7 to 8 hours or until beef is tender.
3Remove beef from slow cooker. Cut beef into thin slices; return to slow cooker. Cover and cook on low heat setting 20 to 30 minutes longer or until beef is hot.
4Layer beef, cheese and bell peppers on bottom halves of focaccia; top with remaining halves. Cut each focaccia into 8 wedges.