Preheat oven to 350 degrees F.
Rinse salmon fillets in cold water, place onto a plate, and squeeze a lemon over the salmon. Sprinkle fillets with salt and black pepper.
Fold a piece of parchment in half cross wise, and center a salmon fillet on one side of the paper. Place 1 or 2 lemon slices on top of the salmon, and surround with sliced sweet potato pieces. Sprinkle 2 tablespoons of geen onion over the lemon slices, and fold the parchment paper over the salmon. Fold the edges of the paper over several times, all around the open edges, to seal the salmon into a parchment paper envelope. (Do not tape the parchment paper closed.) Place the sealed envelopes onto a baking sheet, and brush the tops of each packet with about 1 teaspoon of olive oil.
Bake in the preheated oven until the sweet potato is tender and the salmon is opaque and slightly flaky, 20 to 25 minutes. To serve, place a packet onto a plate, and cut open the paper to release the aroma.