Whisk together the lime juice, garlic, cumin, vegetable oil and chopped chipotles with ½ teaspoon salt. Rub the marinade all over the pork tenderloin and refrigerate for 1 hour.
Preheat oven to 475ºF.
Roast the tenderloin on a foil-lined baking sheet for 20 minutes, or until a meat thermometer inserted at the thickest part of the tenderloin registers a minimum of 145ºF for medium-rare.
Remove the tenderloin from the oven, transfer it to a cutting board and allow it to rest for 10 minutes before slicing into bite-sized pieces. Reduce oven to 400ºF.
Assemble the nachos by layering chips with cheese, black beans, olives and cubes of tenderloin in an oven-safe 13-by-9-inch baking dish. Bake nachos for 5 to 10 minutes, or until cheese is fully melted.
Remove nachos from oven and top with guacamole, salsa and sour cream. Garnish with chopped scallions and serve immediately.
There are two secrets to moist pork tenderloin: don't overcook it and always remove the silverskin prior to roasting. Trim all silverskin (the shiny, fibrous skin) using a sharp knife and long, gliding strokes, avoiding cutting off any of the actual muscle.