Add the olive oil to the slow cooker to coat the bottom of the pan.
Place the onions on bottom topped with the beef and then pour in the mushrooms.
Add the rosemary, basil, thyme, oregano, pepper, garlic, broth, and vinegar.
Place the lid and cook on high for 4 - 6 hours (or 6 - 8 hours on low).
Remove the beef and mushrooms to a serving dish. Place the juices that remain in the slow cooker into a small pan to be used on the stovetop.
Heat the juices over medium high heat.
In a small cup, combine the cornstarch and cold water. Stir well until no lumps remain.
When the broth mixture is almost simmering, slowly stir in the cornstarch mixture. Stir continually until the sauce thickens. Pour the gravy over the meat and mushrooms and serve immediately.