Roast the yams in a little olive oil in a 375-400 oven until soft and a little brown on the outside, about 30 minutes (depending on how big the cubes are). Cool.
Mix remaining ingredients except for the pine nuts and cheese, and toss with the yams. Crumble in the cheese (if the cheese is too soft to crumble, use a fork to help it along; also crumbles better if frozen). Allow to sit in the fridge at least an hour to let the flavours develop (but will last several days in the fridge). Add pine nuts just before serving to keep them crunchy.