In a wide, shallow dish, whisk together 1/4 cup of the vinegar, 1 tablespoon of the marjoram, 1 teaspoon of the salt, 1/2 teaspoon of the pepper and garlic. Add pork and gently massage to fully coat with marinade. Cover and refrigerate about 1 hour. In a medium bowl, combine tomatoes, cucumber, remaining 1 tablespoon vinegar, remaining 1 tablespoon marjoram and remaining 1/2 teaspoon salt. Set aside. Prepare a grill for medium-high heat cooking. Remove pork from marinade and pat dry; discard marinade. Grill, covered, 4 minutes per side until pork reaches an internal temperature of 145°F. Remove from the grill and allow to rest for about 5 minutes before serving. Add chives to salad and toss to combine. Serve alongside grilled pork.