Place the tomatoes and onions in a medium-sized bowl.
In a jar with a tight-fitting lid, combine the garlic, vinegar, parsley, cumin, oregano, thyme, red pepper flakes, and salt and pepper to taste.
Add the olive oil and shake vigorously until emulsified.
Pour over the tomato-onion mixture and toss to combine.
Set aside to marinate while grilling the pork.
Preheat an outdoor grill to medium-high heat.
Lightly coat the pork with olive oil and season it generously with salt and pepper.
Grill the pork until nicely browned on the outside, turning as needed, and cooked to an internal temperature of 145°F—it will be slightly pink in the center.
Let rest for three minutes, then slice crosswise on a diagonal into 1/2-inch-thick pieces.
Shingle on a platter.
Stir the tomato-onion salad once more, taste for seasoning, and then spoon it around the pork.