FOR THE BEEF:Rub all sides of the beef with the vegetable oil, and season with salt and pepper.
Sear in Skillet over high heat for 30 seconds on each side.
TO MAKE THE PONZU SAUCE: In a bowl, whisk together the soy sauce, vinegar, sugar, lemon and lime juices, and ginger juice. Keep whisking until the sugar dissolves.
Slice crosswise with a very sharp knife into 1/4-inch slices, keeping them to an even thickness if possible. Fan the slices, overlapping, on a platter and let stand for 10 minutes. Drizzle with the Ponzu sauce and serve.
NOTE: To make 1 teaspoon ginger juice, grate a 1-inch piece of peeled, fresh ginger on a ceramic ginger grater set over a plate. Transfer the grated ginger and any juice on the plate to a small, fine-meshed strainer and press down on the ginger pulp to extract all its juice.