Heat the oil in a skillet and cook the onions and mushrooms on medium/low for about 5-10 minutes.
Season the brisket well with salt/pepper.
In a large skillet, sear the brisket on both sides to make a brown crust.
Place in slow cooker, fatty side up.
Spread the garlic all over the top.
Pile the onions and mushrooms on top of the meat.
Combine broth, Worcestershire sauce, and Tamari.
Pour this over the meat.
Cook on low 6 hours, remove and slice against grain.
Return to pot on high for 2 hours and shred!
Mmmm!