Preheat oven to 180 C (350 F).
Mix the chia seeds in a small bowl with 2 tbsp of water and set aside.
In a food processor, combine the almonds, buckwheat flour, oats and salt. Blend until the almonds and oats have broken down into flour.
Add in the chia mixture and olive oil then pulse in until combined.
Drizzle in the remaining water a tablespoon at a time while pulsing the mixture until a dough forms (you might not need all of the water). Roll the pastry out on a piece of baking paper until it's only a few mm thick. Cut into 9 cm (~3.5 inch) diameter circles and push each one into the well of a tartlet pan. Bake for 12 minutes until dry. Leave to cool.