For the spicy sauce: Cook the chiles in boiling water until tender, about 20 minutes. Put in the blender with a little of the cooking water and the vinegar and garlic. Season with salt and pepper. Blend until smooth. Set aside.
For the sweet sauce: Using a blender, blend the vinegar, sugar, tomatoes and garlic. Pour into a saucepan and cook until thick, about 30 minutes. Season with salt and pepper. Set aside.
For the pork tenderloin: Preheat the oven to 350 degrees F/180 degrees C. Place the pork in a bowl, add the paprikas and cayenne and mix well.
Heat the oil in a pan over high heat. Add the pork and fry until golden brown on all sides, about 5 minutes. Put the pan in the oven until a meat thermometer inserted in the center of the tenderloin reads 122 degrees F/50 degrees C for medium, about 15 minutes. Place the pork on a plate and cover with aluminum foil. Let rest for 10 minutes and slice.
Place the meat and onions on the rolls. Dip the sandwiches in the spicy sauce and add a ladle of the sweet sauce. Squeeze some lime juice over top.
Recipe courtesy Chuck's Week Off: Mexico