In saucepan of boiling, salted water, cook orzo until al dente, about 7 minutes; drain, reserving 3 tbsp. cooking water. In large skillet, heat oil over high. Cook scallops until browned, 1 to 2 minutes per side. In saucepan, stir orzo, pasta water and mascarpone; season. Divide among plates; top with seasoned scallops, arugula and chives.
Be a Sauce Boss: Save some of that pasta cooking water—a splash of the salty stuff is a great way to loosen any too-thick sauce.