Preheat the oven to 425ºF. Season the pork generously on all sides with salt and pepper.

Heat 2 tablespoons of oil in a large skillet over medium-high heat. Sear the roast on all sides, including the ends, until browned, about 4 minutes per side. Place on a rimmed baking sheet or roasting pan.

Toss the apples with 1 tablespoon of oil and a large pinch each of salt and pepper. Arrange the apples around the roast and bake for 45 minutes or until an instant read thermometer reaches 145ºF. Remove the pork from the pan, cover with foil, and let sit for 10 minutes.

While the pork is roasting, make the sauce: In a small saucepan, combine the honey, mustard, and water. Simmer over medium heat until the sauce thickens slightly, about 2 minutes. Keep warm or reheat briefly before serving.

Heat 1 tablespoon of oil in a large skillet over medium-high heat. Add the mustard greens, a few handfuls at a time. Add a large pinch each of salt and pepper and cook, tossing until wilted, for about 10 minutes. Stir in the vinegar and cook until evaporated. Season to taste with more salt and pepper if needed.

Place the mustard greens on a serving platter. Top with the pork roast and scatter the apples around. Serve the sauce on the side.