Start to finish: 40 minutes
Hands-on time: 30 minutes
1/2 cup thinly sliced red onion
4 ounces feta cheese, crumbled, divided
1/3 cup low-fat buttermilk
1/4 cup mayonnaise (low-fat if you prefer)
1 tablespoon fresh lemon juice
1 tablespoon extra-virgin olive oil, plus extra for brushing the pork
Freshly ground black pepper
1 (1-pound) pork tenderloin, trimmed
11/2 cups 1/4-inch cubed and seeded cantaloupe
3/4 cup 1/4-inch cubed seedless cucumber
3/4 cup fresh mint leaves
3/4 cup fresh cilantro leaves
3 tablespoons fresh lime juice
Preheat the grill to medium.
Set the sliced red onion to soak in ice water for 20 minutes (this will remove their “bite”). Drain and pat them dry and set aside.
Combine half of the feta, buttermilk, mayonnaise, lemon juice, and olive oil in a blender and blend until smooth. Season with pepper and stir in the remaining feta. Set aside.
Brush the pork lightly all over with some oil, season it lightly with salt and pepper and grill it directly over the heat, giving it a quarter turn at a time, until a thermometer inserted at the thickest part registers 140°F for medium, about 2 minutes per side for a total of 8 minutes. Transfer the pork to a plate, cover it loosely with foil and let it rest for 10 minutes.
Toss together the onion, watermelon, cucumber, mint, cilantro, lime juice, and salt and pepper to taste. Add the pork juices from the resting pork to the feta dressing, whisking to incorporate.
Place a mound of the salsa on each of 4 plates. Slice the pork crosswise into rounds 1/2-inch thick and arrange a quarter of the slices on top of each. Spoon the dressing on top of the pork.