Half-fill a large (4-quart) saucepan with water, add 1 tablespoon salt and bring to a boil. Add the potatoes and simmer over medium heat until tender, about 12 minutes. Drain.
Pat the scallops dry with paper towels. Heat a very large (12-inch) skillet or griddle over medium-high (for best results, choose a skillet or griddle that’s heavy and non-stick or well-seasoned cast iron). Add the oil, and, when quite hot, add the scallops in an uncrowded layer. Sprinkle with salt and pepper. Sear, turning occasionally, until golden, only about 2 minutes total. (With high heat, you will be able to sear the scallops without overcooking them.) Scoop onto a wide plate.
Add the chorizo and green onions. Cook over medium heat, breaking up any clumps of chorizo, just until the sausage has rendered its fat, 6 or 7 minutes. Add the drained potatoes and continue cooking, occasionally scraping up any sticky bits, until the potatoes begin to look crusty-brown, about 15 minutes. Meanwhile cut the scallops into pieces that resemble the diced potatoes. When the potatoes are browned, add the scallops. Mix everything together as the scallops heat for a minute or so, then scoop the mixture into a serving bowl and set before your guests.