Rinse the salmon fillets, pat them real dry and place them skin side down on a cutting board.
In a small bowl, mix the pickling salt, coconut sugar, black pepper, fennel seeds, chili pepper flakes and lemon zest.
Divide that salt equally between the salmon fillets and spread it delicately with your fingers all the way to the edge so both fillets get completely covered in salt.
Place the whole bunch of fresh dill on one of the salmon fillets and quickly flip the other one right over to form a sandwich - flesh to flesh, tail to tail.
Wrap the fillets as tightly as you can in plastic wrap, then place the salmon in a ceramic dish that's just large enough to accomodate it. Cover it with a plate and place a weight on top of it, something that weighs about a pound.
Place this entire rig in the fridge and let it rest for 48 to 72 hours, flipping the salmon over once or twice a day. The longer you leave the salmon in the fridge, the more moisture will get drawn out, so the dryer and saltier your gravlax will be.
When you are ready to serve your gravlax, remove the dill and delicately scrape off all the salt mixture with the back of a blade.
With the help of a sharp knife (sashimi knives work wonders for this), carefully remove the skin and slice the fillets on a bias, as thinly as you possibly can.
Keep the leftovers in the refrigerator wrapped tightly in plastic film; consume within a few days.