Bring a large pot of water to a boil. Cook noodles, stirring occasionally, until just tender, 6 to 8 minutes or according to package directions. Drain and transfer to a large bowl.
Meanwhile, whisk miso, mirin, vinegar, canola oil, ginger and garlic in a medium bowl. Add scallops and stir gently to coat. Let marinate for 5 minutes (scallops will begin to break down if marinated longer). Using a slotted spoon, remove the scallops, reserving the marinade for the sauce.
Heat olive oil in a large nonstick skillet over medium-high heat. Add the scallops and cook until golden brown, about 3 minutes per side. Transfer to a plate and cover with foil to keep warm. Add the reserved marinade to the pan and cook over medium-high heat until brown, about 1 minute. Pour the sauce over the noodles, add scallions and toss to coat. Top with scallops and serve immediately.
Ingredient notesMiso: Fermented bean paste made from barley, rice or soybeans used in Japanese cooking to add flavor to dishes such as soups, sauces and salad dressings. A little goes a long way because of its concentrated, salty taste. Miso is available in different colors, depending on the type of grain or bean and how long it's been fermented. In general, the lighter the color, the more mild the flavor. It will keep, in the refrigerator, for more than a year. Mirin: A low-alcohol rice wine essential to Japanese cooking. Look for it in the Asian or gourmet-ingredients section of your supermarket. An equal portion of sherry or white wine with a pinch of sugar may be substituted for mirin.We prefer cooking with "dry" sea scallops (scallops that have not been treated with sodium tripolyphosphate, or STP). Scallops that have been treated with STP ("wet" scallops) have been subjected to a chemical bath and are not only mushy and less flavorful, but will not brown properly.