In a large skillet over medium high heat add the olive oil. Salt and pepper the stew meat and add in batches to sear on both sides until brown, but do not cook throughtout. Add the stew meat to the slow cooker.
Add the beef broth, dry onion soup mix, Worcestershire sauce, onions, mushroom, and garlic. Cook on low for 5-6 hours or high 3-4 hours.
30 minutes before it is done cooking, mix together in a small bowl the water and cornstarch. Stir it into the slow cooker and allow it to thicken.