Start off by sprinkling the salt evenly over the salmon filet. Then, cut into 2" pieces.
Next, cut two pieces of parchment paper about 2' long. The idea is to create a packet so it should be long enough to fold over and completely enclose the fish.
In a small prep bowl add the olive oil, chopped herbs, lemon juice and garlic.
Using a large pan (with a lid) or braiser lay out the parchment paper in a cross pattern.
Create a cross with the parchment paper, laying one 2' piece on top of the other. One laying side to side and one going top to bottom.
Then, place the fish in a single layer. Evenly spread on the olive oil herb mix over the pieces of fish.
Now layer on the onions and lemon slices.
Fold the parchment over and create a packet so no steam can escape.
Here is the important part. Once the parchment packet is all enclosed, place the lid on your pot, Dutch Oven or brasier. Turn the heat on to medium-high. Leave it there for 5 minutes. Then, without opening the lid, lower the temp to medium heat and cook for another 8-12 minutes. For thinner filets remove the lid around the 8 minute mark. If it is on the thicker side, go 12 minutes. It's really important that you do not remove the lid until the time is up! I have been making salmon this way for years and I still worry it won't work. But to my surprise, it does every single time. You have to trust the process. After the time is up, remove the lid and carefully unwrap the parchment to check the salmon.
The salmon is done with the internal temp reaches 145 degrees in the thickest part of the cut or if it is flaky and falls apart easily. If the salmon is not done fold the packet back up, place the lid on and cook for a few more minutes.