Step 1: Trim the pork tenderloins of any silver skin or excess fat. Pat them thoroughly dry with paper towels.
Step 2: In a medium bowl, whisk together the olive oil, soy sauce, Dijon mustard, honey, minced garlic, chopped fresh rosemary, chopped fresh thyme, black pepper, and optional red pepper flakes to create the marinade.
Step 3: Place the trimmed pork tenderloins into a large resealable bag or a shallow dish. Pour the prepared marinade over the pork, ensuring it is completely coated. Seal the bag or cover the dish and refrigerate for at least 30 minutes, or up to 4 hours. Do not marinate longer than 4 hours.
Step 4: Preheat your grill to medium-high heat (approximately 400-450°F or 200-230°C). Clean the grill grates well and lightly oil them to prevent the pork from sticking.
Step 5: Remove the pork tenderloins from the marinade, allowing any excess to drip off. Discard the used marinade. Place the tenderloins directly on the preheated grill grates.
Step 6: Grill the pork for 2-3 minutes per side, rotating to achieve an even sear and distinct grill marks on all four sides of each tenderloin.
Step 7: Reduce the grill heat to medium-low (about 325-350°F or 160-175°C). Continue to grill, turning the tenderloins occasionally, for an additional 10-15 minutes, or until an instant-read thermometer inserted into the thickest part registers an internal temperature of 140-145°F (60-63°C).
Step 8: Carefully transfer the grilled pork tenderloins to a clean cutting board. Tent them loosely with aluminum foil and allow them to rest for 5-10 minutes. This resting period is crucial for juicy results.
Step 9: Slice the rested tenderloins into 1/2-inch thick medallions and serve immediately with your favorite side dishes.