Heat oil in a large cast-iron skillet over medium-high temperature. Add boiled potatoes to skillet and cook, flipping halfway, until golden brown and crispy. Remove from heat; add cider vinegar, salt and pepper to taste. Sprinkle with parsley, and stir to combine. Let potatoes rest in pan while steaks cook.

To make the Chimichurri sauce: In bowl of a food processor, add 1 1/2 cups Italian parsley, nasturtium leaves, mint leaves, garlic cloves, capers, salt and pepper to taste; pulse until herbs are finely chopped.

Meanwhile, grill steaks, flipping halfway, until grill marks develop and meat is medium-rare approx. 6 to 8 minutes per side. Arrange potatoes on a serving platter; top with steaks. Place a heaping tablespoon of sauce on each steak and sprinkle with salt.

Serve immediately, add potatoes with the sauce.