Place the brisket and chopped onion in the bowl of a lightly greased slow cooker.

In a medium bowl, whisk together the ketchup, beef broth, brown sugar, Worcestershire sauce, chilies in adobo, and spices. Pour over the brisket.

Cover and cook on low for 8-10 hours, or until meat shreds easily with a fork. Remove the brisket from the slow cooker and shred. Cover and keep warm.

Pour the sauce from the slow cooker through a fine mesh sieve into a medium saucepan. Simmer for 15-20 minutes over medium heat until sauce thickens and reduces by about half. Toss the shredded meat with the sauce.

While brisket is cooking, caramelize your onions. Heat the butter and oil in a large skillet over medium-low heat. Cook, stirring occasionally, until the onions are dark golden brown. If you make the onions earlier in the day, reheat them before serving.

Slice King's Hawaiian rolls horizontally. Pile beef on the bottom half of the buns. Top with a quarter slice of cheese and some caramelized onions. Add the top half of the bun and enjoy!