For the sauce: In a food processor, add the red wine vinegar, garlic, mint, kale, red onion and a pinch of salt and pepper. Pulse to chop gently, then add the olive oil in a slow stream while still pulsing to get a chunky sauce consistency. Rest at room temperature for about 30 minutes before using.
For the steaks: Heat a grill or grill pan to medium-high heat.
Season the steaks on all sides with salt and pepper, then drizzle with olive oil. Grill the steaks over indirect or direct heat, flipping once, until desired doneness. Remove to a plate and rest under aluminum foil for a real 10 minutes before serving. Serve with the sauce.