In a large skillet over medium-high heat, cook the beef and chorizo together, breaking up the meat with a wooden spoon. When the meats are crumbled, push them to one side of the pan, tilt the pan to collect the oil, then spoon off and discard the oil.
Stir the onion into the meats and cook, stirring, until the onion softens, about 3 minutes. Stir in Stubb’s Original Bar-B-Q sauce and water, reduce the heat, and simmer, stirring occasionally, for 15 to 20 minutes; the mixture is done when it’s moist and glazed, neither dry nor soupy. Taste, and add salt, pepper or vinegar as needed. (The mixture may be made 2 days in advance and refrigerated; reheat before using.) Serve hot, in toasted hamburger buns, with plenty of napkins.