Mix all dry ingredients in a small bowl. Sprinkle generously over roast and rub it really good over roast. Make sure entire roast is covered with the dry mix.
Spray covered roasting pan with pam, then slice first onion and place on the bottom of the pan, then place the roast on top of onions. Slice second onion on top of the roast, then pour liquid smoke and sweet chili sauce on top.
Place the lid on roasting pan and cook the roast until it pulls easily apart. I would check on it after the first hour. then every 30 minutes. It needs to be really tender.
Once it is done let it sit for about 20 minutes then using two forks pull the meat apart until it is shredded add BBQ sauce (warned) and serve anyway you want.