Sprinkle roast with half the salt and pepper. In a Dutch oven, heat oil over medium heat. Brown roast on all sides. Remove from pan to a 6-qt. slow cooker.
Add onion and remaining 1/2 teaspoons of salt and pepper to the same pan; cook and stir until tender, 5-7 minutes. Reduce heat to medium-low. Cook 20-25 minutes, stirring every 5 minutes, until onions are a golden brown color. Add garlic and maple syrup; cook and stir 5 minutes longer. Sprinkle with flour. Add beef broth, stirring to loosen browned bits from pan. Transfer to slow cooker.
Add rosemary and bay leaf to slow cooker. Cover and cook on high until beef is tender, about 6 hours. Remove beef and shred with two forks. Return beef to slow cooker.
Remove bay leaf; discard. Add noodles; stir to coat. Top with Monterey Jack cheese. Cook until noodles are done, 20-25 minutes longer.