Mix the ground flaxseed and water in a small bowl and set aside to make your flax egg.
In a large bowl using a handheld mixer or a stand mixer with the paddle attachment, beat the softened vegan butter, brown sugar and granulated sugar for 1-2 minutes until creamy.
Mix in the flax egg and vanilla, scraping the sides of the bowl as needed.
Stop the mixer and add the flour, oats, baking soda, cinnamon and salt. Turn the mixer on low speed and mix until just combined. Stir in the chocolate chips until fully incorporated.
Cover the bowl and refrigerate the cookie dough for 30 minutes before baking.
About 10 minutes before the dough is done chilling, preheat the oven to 350 degrees F and line two cookie sheets with parchment paper or lightly spray with oil.
Using a cookie scoop or spoon, scoop about 1.5 tablespoons of dough onto the prepared baking sheets, leaving a little room between each one. Press each ball down gently to slightly flatten them, as these cookies won't spread very much in the oven.
Bake for 11-13 minutes, until the tops of the cookies are set.
Let cool on the cookie sheet for 5 minutes, then transfer to a cooling rack. The cookies will firm up as they cool. Enjoy! Cookies will keep at room temperature for 3-4 days in a covered container.