Preheat grill to medium-high heat.
Season the steaks with salt and pepper on both sides.
In a small bowl, whisk together the olive oil, red wine vinegar, Dijon mustard, capers, garlic, parsley, and red pepper flakes (if using). Set the vinaigrette aside.
Brush the grates of the grill with oil to prevent sticking.
Place the steaks on the grill and cook for 4-5 minutes on each side for medium-rare, or longer for desired doneness. Baste the steaks with the vinaigrette during the last few minutes of cooking.
While the steaks are cooking, place the tomato halves on the grill, cut side down. Grill for 2-3 minutes until slightly charred.
Remove the steaks and tomatoes from the grill and let the steaks rest for 5 minutes.
Slice the steaks against the grain and place on a platter. Arrange the grilled tomatoes around the steaks.
Drizzle the remaining vinaigrette over the steaks and tomatoes.
Serve hot and enjoy the deliciousness!