Preheat oven to 325 degrees F. Grease two cookie sheets or line with parchment paper and set aside.

In the bowl of a stand mixer fitted with a paddle attachment or a hand mixer, beat together the vegan butter and sugars in a large bowl on medium speed until light and fluffy, about 2 minutes. 

Add the ground flax seed, water, vanilla, and lemon juice. Mix together on medium until incorporated. 

Add flour, oats, baking soda, salt, and ground cinnamon. Mix on medium speed just until dough comes together and no flour streaks remain. 

Add the chocolate chips and chopped walnuts, stir until incorporated throughout. 

Scoop dough out and form into cookies about 2-3 tablespoons big. Place on prepared baking sheets and space about 2 inches apart. 

Bake for 15-17 minutes, until cookies are golden brown. 

Allow to cool before serving. Store at room temperature in a sealed container for up to a week.