Combine the oil, vinegar in a bowl and season with salt and pepper. Pour half into a jug and reserve for a dressing later. Add the chilli flakes and pork to the remaining oil mixture and toss to coat.
Heat a cast iron grill plate or large non-stick frying pan over a medium-high heat. Add the pork and cook for 3 to 4 minutes each side until cooked to your liking. Transfer the steaks to a plate, then rest, covered with foil for 5 minutes.
Meanwhile, add the kale to the pan or grill. Cook for 2 minutes, turning until lightly charred and just wilted. To make the gremolata, combine the parsley, orange zest and garlic in a small bowl.
Serve the steaks and kale drizzled with the reserved dressing and the mashed potato sprinkled with gremolata.