Put all of the seeds into a large mixing bowl. Add 1Tbsp salt (I use unrefined sea salt) and enough filtered water to cover the seeds so they are about 3cm below the water level. Leave them to soak overnight (8 hours or so). In the morning, drain the seeds in a sieve and rinse them under running water.
Preheat the oven to 160°C (oven bake, no fan).
Tip the strained seeds back into the mixing bowl. Add ½tsp salt, 1½ Tbsp psyllium husk and 250mL (1 cup) water, and stir it all together thoroughly. Leave it for ~10mins to let it set into a sloppy jelly. If it is too runny, add some more psyllium husk - I would suggest up to ½Tbsp (so you have total 2Tbsp psyllium husk in your cracker mix).
Spread the cracker mix on a silicone baking mat on a large flat baking tray. Bake for 1 hour. After about an hour, take the tray out of the oven and flip the silicone mat over (it will be extremely hot so use oven mitts!), then carefully peel the silicone off the cracker. Sometimes I find that the edges are browned and crispy already so I break them off now and continue baking the rest. Return the upside down cracker to the oven on a reduced heat just to crisp it up and brown it. Keep an eye on it now because you don't want it to burn.
When it's all nicely browned and crispy, remove from the oven and let it cool. Break into smaller pieces and store in an airtight container.