For maximum flavour and moisture, marinate the pork for six to 12 hours. And let cooked meat rest for 10 minutes before cutting it to allow the juices to redistribute. Watching your sodium intake? Look for low-sodium feta, and rinse the olives before adding them to the salad.
Trim pork of any excess fat and place pork in a large freezer bag. In a small bowl, mix together marinade ingredients and pour into bag. Seal bag and let sit in the refrigerator for as much time as possible'six to 12 hours if you can.
Brush each pepper slice with a little olive oil, and season with salt and pepper to taste. Place on preheated, medium-high grill skin-side down until skin blisters and flesh softens, approximately six minutes. Turn over and cook for six minutes more. Remove from grill, place in a small bowl and tightly cover with plastic wrap for five minutes.
Peel off and discard skin from peppers. Cut peppers into 1-in.-square pieces. Set aside. Meanwhile, brush onion slices with a little olive oil, season with a pinch of salt and pepper, and grill for six minutes on each side until tender and flesh is caramelized. Remove from heat, cool and cut each ring in quarters.
In a medium bowl, toss together peppers, onions, olives, feta, lemon zest, basil leaves, balsamic vinegar and remaining olive oil. Adjust seasoning to taste. Set aside.
Remove pork from marinade and place on grill (discard marinade). To cook thoroughly, rotate tenderloin while grilling. Cook until internal temperature reaches 160°F, about 15 minutes. Let sit for 10 minutes before slicing. Serve with grilled Greek salad on the side.
Per serving: 353 calories, 30 g protein, 16 g fat (3 g saturated fat), 23 g carbohydrates, 2 g fibre, 87 mg cholesterol, 613 mg sodium