Cube the beef. Slice the onion, mushrooms, and bacon.
Add the beef, bacon slices, mushrooms, onion slices, and beef broth to a large resealable freezer bag.
Add the bag contents to the Crock-Pot and cook on low for 4-6 hours.
If you want to thicken up the gravy, mix together 2 Tbsp. of cornstarch with 1/4 cup of water and stir into the beef mixture in the slow cooker 20 minutes before serving.
*If you want crunchier bacon, you can fry it before adding it to the freezer bag.