Make the marinade: combine 4 tbsp olive oil, garlic powder and coarse salt in a bowl.
Rinse and pat dry the pork tenderloins. Place the pork in a large sealable plastic bag, then pour in the marinade. Toss gently to coat, then place in refrigerator. Marinate refrigerated for 1 to 2 hours, then take the pork out refrigerator to marinate at room temperature for about 20 minutes.
Make the cilantro pesto as the pork marinates. Combine the 2 garlic cloves, cilantro, lime juice, red pepper flakes and 1/3 cup olive oil in a food processor. Puree until the cilantro and garlic are finely chopped and everything is well mixed together. Transfer the pesto into a bowl for serving.
Preheat a grill to medium high. Coat with oil spray. Shake the excess marinade from the pork, then place the pork on the grill. Grill covered for 8 minutes, then turn to grill for another 8 minutes.
Check the pork for doneness after 16 minutes of grilling; it will take about 16 to 20 minutes depending on your grill and thickness of the pork. Pork tenderloin should be cooked to 145 degrees internal temperature; a bit of pink is fine.
Let the pork rest for 5 minutes, then slice into 1/2 inch thick pieces. Plate several slices along with some cilantro pesto and enjoy!