Sprinkle pork on all sides with 1/8 teaspoon of the salt and 1/4 teaspoon of the pepper.
Heat 1 teaspoon of the oil in a large heavy skillet over medium-high heat.
Add the pork and cook, turning once, until the pork is well browned and internal temperature reaches 145 degrees F, about 1 1/2 minutes on each side. Transfer pork to serving platter and cover to keep warm.
Add the remaining 1 teaspoon oil to skillet.
Add garlic and cook, stirring constantly, until garlic is fragrant, about 30 seconds.
Add the broth and increase heat to high and cook, stirring to scrape up the browned bits from the bottom of the skillet, until the liquid is reduced by two thirds, about 5 minutes.
Remove the skillet from the heat and stir in the remaining 1/8 teaspoon salt, remaining 1/8 teaspoon pepper, the lemon zest and juice, and the parsley.
Serve the pork medallions drizzled with the sauce (makes a generous 1/3 cup; about 1 1/2 tablespoons per serving).