More than three-quarters of Americans report they enjoy eating ethnic food when dining out. The problem is, they say, finding authentic fare. But what many forget is all ethnic cuisine is really a fusion of the indigenous foods of a place with those of the traders and invaders who have passed through.  Each group of outsiders brings new crops to a region and different ways to use the local ones. Traditional cooking methods are modified to accommodate newly acquired utensils and techniques, while commercially made foods eventually replace homemade.