1. Rinse roast, and pat dry. Cut a 1-inch-deep cavity in the shape of an "X" on top of roast. (Do not cut all the way through roast.) Dredge roast in all-purpose flour; shake off excess.
2. Cook roast in hot oil in a Dutch oven over medium-high heat 1 to 2 minutes on each side or until lightly browned.
3. Place roast in a 6-qt. slow cooker. Stuff cavity with sliced red onion and minced garlic; top roast with potatoes and baby carrots. Pour beer, balsamic vinegar, and Worcestershire sauce into slow cooker. Sprinkle with parsley, bouillon, and ground pepper. Add bay leaves to liquid in slow cooker.
4. Cover and cook on LOW 7 to 8 hours or until fork-tender. Shred roast using two forks. Season with salt to taste. Serve in Toasted Bread Bowls, if desired.
*3 cups low-sodium beef broth may be substituted.