How to Make It
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 medallions with salt and pepper, add them to the skillet and cook over moderately high heat until well browned on the outside and medium within, 3 to 4 minutes per side. Transfer the medallions to a plate and keep warm.
Add the balsamic vinegar to the skillet and cook until nearly evaporated, scraping up any browned bits from the bottom of the skillet. Add the arugula and toss until wilted, about 2 minutes. Add the tomatoes and the prosciutto and garlic. Cook over high heat for 2 minutes, stirring occasionally; season with salt and pepper. Transfer the arugula to a platter, top with the pork and serve.