Remove any visible fat from the pork and dust the tenderloin with the salt and pepper. In a small saucepan, combine the tomato sauce, mustard, Tabasco, brown sugar, garlic, and onion and simmer for 20 minutes.
Be careful not to boil. Coat the grill with cooking spray and preheat for 5 minutes. Grill the tenderloin for 2 minutes. Generously cover the pork with the sauce. Continue grilling for 2-4 minutes.
To serve, slice thinly across the grain of the meat and cover with additional warm barbeque sauce.