For the sauce: stir together all sauce ingredients in a bowl until combined, then chill, covered, until ready to use. For the pork: put oven rack in middle position and preheat oven to 350 degrees. Cut pork crosswise into 1-inch thick slices medallions. Whisk together flour, salt, and pepper in a shallow bowl. Whisk together eggs with a pinch of salt in another shallow bowl and put breadcrumbs in a third shallow bowl. Working with 1 medallion at a time, dredge them in flour, shaking off excess, and dip in egg, letting excess drip off, then coat with crumbs, pressing to help them adhere. Arrange pork in 1 layer on baking sheet. Heat 1/4-inch oil in a 12-inch heavy skillet over moderate heat until hot but not smoking, then panfry medallions, turning over once, until golden brown, 6-8 minutes total. Transfer to a clean baking sheet and roast in oven until thermometer inserted horizontally into center of meat registers 145-150 degrees, 6-7 minutes. Serve pork with sauce, lemon wedges and watercress.
Ready in 30 min