1) Scrub fingerling potatoes and put in single layer in glass microwave safe baking dish.
2) Cover dish with plastic wrap, secure to edges, cut holes in top with knife to vent.
3) Microwave on high for 5 to 7 minutes or until potatoes are fork tender. Remove from microwave and let stand for 5 minutes.
4) Cut each fingerling potato in half and place (insides facing up) on broiler pan.
5) Coat each potato with melted butter, salt & pepper, then cheese.
6) Put under broiler for 2 to 3 minutes or until cheese melts. Remove from oven and sprinkle onion pieces over the top.