Throughly clean and wash the salmon. Place salmon on heavy-duty aluminum foil. Stuff salmon with the sliced onions, butter, salt and pepper. Also smear butter on the outside of the salmon plus squeeze the lime juice over as well. DO NOT REMOVE THE SKIN OF THE SALMON. Sprinkle with more salt and pepper. Wrap the salmon tightly in the foil so as to make as "air-tight" as possible...usually two layers of foil. Place on the hot Bbq for 25 - 30 minutes then turn over and bake the otherside for 15 minutes. Remove from Bbq and serve with "new" mint potatoes and fresh peas. This is absolutely delicious!