Add all the dry ingredients to the bowl of a food processor and whizz for a few seconds until the oats look like coarse flour.
Add the oil and whizz again, then gradually add enough boiling water until the dough comes together in clumps (around 4 tablespoons).
Roll the dough out very thinly (about 2mm). The easiest way to do this is to roll it out between 2 sheets of greaseproof paper or silicon. Cut into squares approximately 7 cm, you should end up with around 16 biscuits.
Slide the greaseproof paper with the biscuits onto a baking tray and bake for 30 mins at 160 degrees. Check after 20 minutes and turn the tray if necessary.
Allow to cool for 10 minutes on the tray, then remove with a palette knife. Finish cooling on a wire rack.
Store in an airtight tin.
Notes
Variations: use another healthy oil if you prefer. You could also add dried herbs such as rosemary or thyme, dried garlic or a pinch of paprika.If you want chunkier crackers, blitz the oats slightly less. For a smoother texture, process for longer.