1. Combine the 2 tablespoons oil, 1 teaspoon salt, the jalapeno flakes, and orange and lemon peels in small bowl. Spread mixture over pork; wrap and marinate in the refrigerator 1 to 24 hours.
2. Meanwhile for tomatoes heat oven to 350 degrees F. Arrange tomatoes halves (cut side up) and garlic on a jelly-roll pan. Drizzle tomatoes with 2 tablespoons oil. Bake until tomatoes and garlic are very soft and tomatoes are lightly brown on bottoms, 1 hour. Cool tomatoes and garlic slightly; peel garlic. Transfer tomatoes and garlic to cutting board and coarsely chop. Transfer tomatoes, their juices, and garlic to small saucepan. Stir in salt and vinegar. Set aside.
3. Heat and oil grill or grill pan. Grill pork 20 minutes, turning several times, until meat thermometer inserted in the thickest part of the tenderloin registers 155 degrees F.
4. Ten minutes before pork is done, cook tomatoes over low heat just until heated through. Transfer pork to a cutting board; cool 5 minutes. Slice tenderloin and serve with tomatoes. Garnish with sliced lemon and thyme sprigs, if desired. Makes 5 servings.