Mix maple syrup, jalapeño sauce, chopped onion, salt and pepper in a bowl to make the marinade.
Wash the pork loin. Using a sharp knife, cut a pocket lengthwise into the centre of the loin. Fill with feta cheese and finely chopped fresh herbs. Close the pocket with toothpicks. Refrigerate in the marinade for 8 hours.
Wrap the pork loin with bacon strips and secure with toothpicks.
Heat the grill to medium-high. Grill the pork over direct heat for 3-5 minutes, turning to brown all sides. Move to indirect heat (away from direct flames), cover with the grill lid, and cook for 45-60 minutes until the internal temperature reaches 63°C (145°F). Rest for 5 minutes before serving.