Place 2 large pieces of tin foil down. Spread sliced onion pieces from one onion, on tin foil the length of the salmon pieces. Lay salmon fillet pieces on top of the onion slices. Salt and Pepper to taste. Lightly spread butter on salmon.
Sprinkle brown suagr over salmon and cover with remaining onion slices. Cover salmon with two pieces of tin foil and crimp sides together.