How to Make It
Heat oil in a large high-sided skillet over medium. Sprinkle pork with 1/2 teaspoon salt and 1/2 teaspoon pepper. Add pork to pan; cook, turning occasionally, until browned on all sides and a meat thermometer inserted into thickest portion registers 145°F, about 15 minutes. Remove pork from pan; keep warm.
Add mushrooms, onions, thyme, remaining 1/2 teaspoon salt, and remaining 1/4 teaspoon pepper to pan; cook, stirring and scraping pan to loosen browned bits from bottom of pan, until vegetables are soft, about 7 minutes. Cut pork crosswise into thin slices; serve with mushrooms and onions.