Preheat an oven to 350 F. Line two baking sheets with parchment paper. Combine the peanut butter, melted coconut oil, chia seeds, water, powdered sweetener, and vanilla extract in a medium-sized mixing bowl. If your peanut butter is on the drier side, feel free to add 1-2 tbsp more melted coconut oil. Mix well to combine.
Next, add in the almond flour, coconut flour, and kosher salt. Mix well to combine. The dough should be thick. Allow the dough to sit for 5 minutes to allow the chia seeds to hydrate.
Use a 1 oz cookie scoop to press the cookie dough into, and then release each scoop onto the baking sheet. These cookies will not spread much at all; you only need to leave enough room to press the cookies down with a fork. You should be able to fit half of the batch of cookies onto the baking sheet.
Press the cookies down in either direction with a fork (one press and then another perpendicular to the first). Bake the cookies for 10-11 minutes or until lightly browned. Store in an airtight container at room temperature for up to a week.