Squeeze the juice from 6 of the limes to make about 1 cup. Place the scallops in a nonreactive deep bowl (ceramic, glass, or stainless steel) and cover with the lime juice. Let marinate for 1 hour.
Drain the scallops and pat dry. In a large bowl, combine with the chopped tomato, onion, avocado, oregano, and the freshly squeezed juice of the remaining lime. Season with salt and serve.