You could try describing it as:
* Pork face and ears salad (this is a literal translation, but not very appetizing)
* Grilled and seasoned pig face and ears (more accurate but still not very appealing)
* Filipino pork and sour meat dish (more general, but captures the essence of the dish)
The best way to explain sisig is to describe its ingredients and preparation: "It's a Filipino dish made with grilled and chopped pork face and ears, seasoned with onions, chilies, and calamansi juice. It's often served sizzling on a hot plate with a raw egg on top."
Ultimately, the best way to understand sisig is to try it yourself!