Season the brisket generously with salt and pepper on all sides.
Coat and rub in olive oil.
Place all ingredients in the crockpot.
Cover and leave on low for 6-8 hours or high for 3-5 hours.
Once cooked (has reached an internal temp of 165℉) , remove the brisket from the crockpot and let it rest for 10 minutes before slicing.
Serve slices of brisket over the onions and drizzle with any remaining BBQ sauce from the crockpot.