Line a baking sheet with parchment paper.
Mix the sunflower seeds, pumpkin seeds, flaxseeds, chia seeds, sesame seeds, and fine salt in a medium bowl.
Pour in the boiling water and stir well. Let sit for 15 minutes to thicken, stirring once halfway through.
Preheat the oven to 280°F or 130°C fan.
Spread the seed mixture into a very thin rectangle, about 15 x 10 inches, on the prepared baking sheet.
Sprinkle evenly with everything bagel seasoning and score into an 8 x 4 grid.
Bake for 40 to 45 minutes, until lightly golden around the edges and firm.
Flip the crackers and bake for another 15 to 20 minutes, until dry and crisp.
Cool completely on the baking sheet.
Snap or cut along the score lines into 32 crackers.