Pat the pork dry and season generously with salt and pepper. Preheat a large cast-iron skillet over medium-high heat for 5 minutes. Add the oil and then the pork. Scatter the shallots, fennel wedges, and thyme around the chops. Cook, flipping the pork and tossing the vegetables halfway through, about 8 minutes total. The pork should be cooked through and well browned, and the vegetables should be tender. Using tongs, remove the pork and vegetables to a plate. Cover and keep warm.
While the pork and vegetables are cooking, make the watercress salad: Using a mandoline, thinly shave the radishes and remaining fennel. Toss the shaved vegetables and watercress with1 tablespoon of the vinegar and a drizzle of oil. Season with salt and pepper. Set aside.
Add the remaining ⅓ cup (75 ml) vinegar to the skillet. Using a rubber or wooden spoon, scrape up any browned bits that are stuck to the bottom of the pan. Stir in the mustard, honey, and ¼ cup water. Simmer until you have a reduced, syrupy sauce. Remove the pan from the heat. Return the pork to the pan and evenly coat with the sauce.
Plate the pork with fennel and shallots and spoon with the pan sauce. Top the pork with a handful of watercress salad. Garnish with the reserved fennel fronds and finish with a pinch of flaky salt
