Trim the excess fat from the brisket and cut it in half width wise.
Combine the next 7 ingredients and rub all over the entire brisket.
Place one half of the brisket on a sheet of foil. Sprinkle half of the liquid smoke over it, making sure to get both sides. Wrap tightly and place into the slow cooker. Repeat with the second half.
Cook the brisket on low for 8 to 10 hours or until fork tender.
To assemble the sandwiches. Start by spreading mayo on the bottom bun, add a layer of meat, a slice of smoked gouda, barbecue sauce and fried onions. Add the top half the bun and enjoyl