Pre heat the oven to 180℃/350℉.
In a high speed blender mix the water and spinach, scraping the sides until pureed. Thermomix 1 minute, speed 5 (you will need to scrape the sides quite a few times).
Add the olive oil, sea salt, sugar, baking powder (and any optional ingredients) and mix together until combined. Thermomix 20 seconds, speed 4.
Add the flour and mix until a dough the consistency of play-doh forms (so it holds together but doesn't stick to your hands).
IMPORTANT - All whole flours are slightly different in the rate they absorb water. This is the reason white (highly refined flours) are used in processed foods because they bring consistent results. So you may need to adjust the amount of flour (or water) slightly to achieve the right consistency as described above (especially with the GF variation below).
Form into a rough disc, place between two sheets of baking paper (or silicone sheets). I use 'If you Care' brand of baking paper, it's very non stick and can even be reused (it's that good).
Roll until VERY thin (1-2mm). If they aren't thin enough they won't crisp up so keep rolling until the dough stops expanding. Remove the top piece of parchment and cut the dough with a pizza cutter or plastic ruler (my new way to get the squares nice and even).
Lift this carefully onto a baking tray.
Bake for 20-25 minutes. I find the outside rows cook quicker than the inside squares so I often take it from the oven at 20-25 minutes, remove the outer rows and return the middle crackers which are still not crisp enough to the oven for 5 minutes or until they are dry and crunchy.