1 1/2 pounds pork tenderloin, sliced crosswise 1 inch thick
Salt and freshly ground pepper
2 tablespoons balsamic vinegar
1 pound arugula, large stems discarded, leaves chopped
1 pound plum tomatoes, chopped
In a very large skillet, heat the olive oil. Add the prosciutto and garlic and cook over moderate heat, stirring, until the garlic is golden, about 4 minutes. Transfer to a plate.
Season the pork slices with salt and pepper and add them to the skillet. Cook over high heat until well browned on the outside and medium inside, 3 to 4 minutes per side. Transfer the medallions to a serving platter and keep warm.
Add the balsamic vinegar to the skillet and cook, scraping up any browned bits, until nearly evaporated. Add the arugula and toss until wilted, about 2 minutes. Add the chopped tomatoes and the prosciutto and cook over high heat for 2 minutes, stirring occasionally; season with salt and pepper. Spoon the mixture over the pork medallions and serve.