Combine olive oil, garlic, orange juice, marjoram, and orange zest in a resealable plastic bag; add tenderloins, seal, and marinate, refrigerated, overnight.
Preheat a grill pan over medium-high heat. Remove tenderloin from marinade, discarding marinade. Wipe excess marinade from pork and season with salt and pepper. Add pork to grill and cook, turning every 4 minutes, until grill marks appear and internal temperature of pork reaches 135 to 140 degrees on an instant-read thermometer, about 21 minutes total. Set aside and let cool completely.
Slice cooled pork crosswise into thin slices. Serve with fruit salsa.