You'll need all-natural cedar plank to infuse the pork with a delicious smoky flavor. You can also turn off the center burner on a gas grill for a portion of the cooking time to keep it from burning.
Soak a cedar plank in water overnight. (Weigh it down with cans or something else heavy to keep it submerged.)
Heat grill to medium, and brush grates clean. Season pork with salt and pepper.
Place pork on soaked cedar plank. Grill pork on plank over direct heat with lid closed (the grill should reach 425 degrees on a grill thermometer), until an instant-read thermometer inserted into the center of the pork loin reaches 138 degrees, 50 to 55 minutes.
Remove pork from plank and let rest for at least 10 minutes before slicing. Serve warm or at room temperature with salsa.
It's important to soak the wood in water overnight to reduce the likelihood of flare-ups; keep some water nearby just in case it catches fire.