Preheat your oven to 350°F (175°C). Line your baking sheet with parchment paper to create a non-stick surface for the crackers.
In a mixing bowl, combine the sunflower seeds, flax seeds, chia seeds, and furikake. Mix well to ensure the seeds are evenly distributed.
Add the sliced scallions or minced shallots, minced garlic, and red chile flakes to the seed mixture. Stir to combine all the ingredients thoroughly.
Pour in the cold water and mix until all the ingredients are fully incorporated. The mixture should be thick but spreadable. If it feels too dry, add a little more water, a teaspoon at a time.
Transfer the seed mixture to the prepared baking sheet. Using a spatula or the back of a spoon, spread it evenly across the parchment paper to your desired thickness. Aim for about 1/4 inch thick for a perfect crunch.
Generously sprinkle flaky sea salt over the top of the mixture. This will enhance the flavor and provide a nice contrast to the nutty seeds.
Place the baking sheet in the preheated oven and bake for about 25-30 minutes, or until the edges are golden brown and the top is firm to the touch. Keep an eye on them to prevent burning.
Once baked, remove the crackers from the oven and allow them to cool completely on the baking sheet. Once cooled, break them into pieces or cut them into squares for serving.