Heat a drizzle of oil in a large pan over medium-high heat. Add pork and cook to desired doneness, 5-7 minutes per side. Remove from pan and set aside on a plate to rest. Wipe out pan. Melt 1 TBSP butter in same pan over medium-low heat. Add scallion whites and cook, stirring, until just softened, about 1 minute. Whisk in stock concentrate, mustard, honey, and ½ cup water. Simmer until reduced, 2-4 minutes.