In a large mixing bowl, or bowl of a stand mixer, combine the coconut oil, brown sugar, and white sugar. Mix for about 2 minutes.
Add in the egg and vanilla extract and stir until just combined.
Add the oats, flour, flaxseed, baking soda, cinnamon, and salt, and mix until combined.
Stir in the chocolate chips.
Form the cookie dough into 1.5 to 2 TBS sized balls and place on a cookie sheet lined with a silicone liner or parchment paper. Top with more chocolate chips if desired.
Cover the pan with plastic wrap and refrigerate or at least 1 hours or up to 5 days. This will help the cookies not to go flat. If you chill them longer than 1 hour it's possibly your cookies won't spread very much as they bake, so you can flatten the balls a bit with your hand before baking.
Preheat oven to 350 Fahrenheit. Line 2 baking sheets with a silicone liner or parchment paper.
Place the cookie dough balls 2 inches apart on the prepared cookie sheets.
Bake the cookies for about 9 minutes or until edges and top are just beginning to set. Do not bake longer than 10 minutes to ensure the cookies are still soft. They will continue to cook on the pan, and will firm up as they cool.
Let the cookies cool for 5 minutes before transferring them to a cooling rack.
The cookies can be stored in an airtight container for up to 1 week, or frozen for up to 2 months.