Set a wire rack in a broiler-safe rimmed baking sheet and mist it with cooking spray.
In a medium bowl, stir together the yogurt, vinegar, oil, oregano, garlic and 1 teaspoon each salt and pepper.
Measure ¼ cup of the mixture into a small bowl and stir in 1 tablespoon water; set aside for serving.
Add the pork to the medium bowl and mix until evenly coated.
Thread the pork, alternating with the tomatoes, onto four 8- to 10-inch metal skewers.
Place the skewers on the prepared rack, spacing them evenly apart. Let stand at room temperature while the broiler heats.
Heat the broiler with a rack about 4 inches from the element.
Broil the skewers until lightly charred, 4 to 6 minutes.
Remove from the oven, flip and broil until charred on the second sides, another 4 to 6 minutes.
Serve with the yogurt sauce.
