Place all the salsa ingredients in a medium bowl and stir gently with a rubber spatula. Cover and refrigerate.
The salsa can be made up to 4 hours ahead. Note: If fresh pineapple is unavailable, you can use frozen, no-sugar-added pineapple chunks, thawed and cut into dice.
When you’re ready to cook, light your grill and set it up for direct grilling.
Preheat to medium high.
Brush and oil the grill grate.
Prep each tenderloin by removing any silverskin, the strip of tough connective tissue that runs the length of the tenderloin.
Use the tip of a fillet knife to lift up one end, which you can then hold on to as you move the blade under the rest of the strip to separate it from the meat; discard.
Rub each tenderloin on all sides with olive oil. Season with the garlic salt and black pepper.
Arrange the tenderloins on the grill grate and grill for about 3 minutes per side (12 minutes total) until an instant-read meat thermometer reaches 145°F. (The pork will still be slightly pink.)
Transfer to a cutting board and let rest for 5 minutes.
Slice into medallions and shingle on a platter.
Serve the pineapple salsa on the side.
Note: As an alternative, you can sear the tenderloins in olive oil in an oven-safe skillet until they’re nicely browned, then transfer the skillet to a 350°F oven to finish for about 15 minutes.