Prepare seed mixture: Grind flax, chia, and hemp seeds to make 1 cup total. Combine with 1/2 cup of whole chia seeds and shelled hemp seeds in a bowl.
Add water and soak: Add 3/4 cup water to the seed mixture. Mix well and let sit for 10-15 minutes until a gel-like consistency forms.
Add optional flavorings: If desired, mix in optional ingredients like garlic powder, chili, nutritional yeast, or salt for extra flavor.
Roll out dough: Place the mixture on a sheet of baking paper. Cover with another sheet and roll out evenly with a rolling pin until thin for crispiness.
Cut crackers: Peel off the top baking paper and cut the dough into desired cracker shapes using a knife or pizza cutter.
Bake crackers: Transfer the crackers on the baking paper to a lined baking tray. Bake in a preheated oven at 200°C (390°F) for 30 minutes, flipping halfway through for even crisping.
Cool and store: Let the crackers cool completely to crisp up further. Store in an airtight container for up to 2 weeks.