Preheat oven to 350F (180°C) and line a cookie tray with baking paper.
Add the almond flour, baking powder, and salt to a medium mixing bowl and whisk together. Make sure there are no "lumps" of flour left.
Make a "flax egg" by mixing the 1 tbsp. flax powder and 3 tbsp. water together in a small bowl and let sit for 5 minutes.
Add the flax egg, pumpkin puree, melted coconut oil, and vanilla extract to a bowl and whisk together until smooth.
Add the brown granulated erythritol to the wet ingredients and stir in well. Most of the sweetener granules should be dissolved.
Add the mixed wet ingredients to the almond flour mixture and stir well to combine. The dough should stick together well but have a similar texture to regular cookie dough.
Depending on the moisture content of your pumpkin puree, add more almond flour (1/4 - 1/2 cup if needed) until the dough can be shaped into a ball. Let the dough sit for 5 minutes before moving on to the next step.
Oil your hands and roll the keto pumpkin cookie dough into balls using 2 tbsp. of dough at a time. You should end up with 12 - 15 cookie dough balls. Press down with a fork crosswise until they're about 1/2 inch (1 1/2 cm) thick.
Bake for 15 - 20 minutes at 350F (180°C) until just starting to brown and turn golden. Remove from the oven and sprinkle with some brown erythritol and cinnamon while warm. Allow to cool on the cookie tray for 20 minutes before carefully moving them to a wire cooling rack until they have completely cooled down.
Once the cookies have fully cooled down, they are ready to be served.
Store in an airtight container for up to 5 days to keep fresh.