In a mixing bowl, combine the salt and the sweet BBQ sauce. Place the salmon, skin side down, on several large sheets of plastic wrap. Cover the entire salmon with the curing mixture, packing the cure into the salmon. Wrap the salmon completely and tightly in the plastic wrap and place the salmon, skin side down on a 1/2 sheet pan. Place something heavy like a skillet, weights, or a brick wrapped in plastic wrap on top of the salmon. This will help infuse the salmon into the mixture. Refrigerate the salmon for 24 hours. In a large saute pan, heat the oil. Add the sausage and brown for 2 to 3 minutes. Add the onions. Continue to cook for 1 minute. Add the potatoes. Season with salt and pepper. Saute for 3 to 4 minutes. Remove from the heat and stir in the garlic, green onions and chopped egg. Set aside and keep warm. Remove the salmon from the refrigerator and wipe off the salt mixture. Rinse the salmon under cold water, removing all the cure. Using a sharp knife, slice the salmon diagonally paper thin. To serve, mound some of the potato mixture in the center of the plate. Place the BBQ salmon gravlax on the croutons and place around the potato mixture.