Combine all-purpose flour and matcha green tea powder in a large bowl. Sift both the flour and the matcha powder.
In a small bowl, mix together the flax meal and water. Whisk until smooth and let it sit for a few minutes until it thickens slightly.
Meanwhile, in a stand mixer with the paddle attachment or in a large bowl with a hand mixer, beat the softened coconut oil, powdered sugar and salt until soft and creamy. Scrape down the bowl as needed.
Add the flax eggs to the coconut oil mixture, and mix well until combined. Gradually add the flour and matcha green tea powder mix and blend until the dough is smooth.
Cut the dough in half and shape into 2 cylinders, about 1.5 inches (4 cm) diameter, 7" (18 cm) long.
Wrap the logs in plastic wrap and chill in the refrigerator until firm, at least 2 hours (or overnight).
Useful tip: you can place the logs on a bed of rice while chilling. It’ll keep the dough in a nice cylindrical shape, so your cookie slices won’t be flat on one side.
Preheat the oven to 350ºF (175ºC). Line the baking sheet with parchment paper or a silicone baking liner. Remove the dough from the plastic wrap, and with a sharp knife, slice the dough into ⅓ inches (7 mm)-thick rounds. Place them on the baking sheet, leaving about 1” (2.5 cm) between rounds.
Bake the cookies at 350ºF (175ºC) for about 15 minutes, or until the edge of the cookies starts to get slightly golden brown.
Remove from the oven and let cool on the baking sheet for 5 minutes; then carefully transfer to a cooling rack and let cool completely.