Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a small bowl, mix together 1 tablespoon of ground flaxseed with 3 tablespoons of water. Allow it to sit for a few minutes until it thickens and becomes gel-like. This will be your flax egg.
In a medium-sized bowl, whisk together the flour, baking soda, baking powder, ground cinnamon, and salt. Set aside.
In a large mixing bowl, cream together the softened vegan butter, brown sugar, and granulated sugar until well combined.
Stir in the prepared flax egg and vanilla extract into the butter and sugar mixture until smooth.
Gradually add the dry ingredients to the wet ingredients, mixing until a cookie dough forms.
Gently fold in the diced apples and, if desired, the rolled oats and chopped nuts. The optional ingredients add texture and flavor.
Drop rounded tablespoons of cookie dough onto the prepared baking sheet, leaving some space between each cookie.
Bake in the preheated oven for approximately 12-15 minutes, or until the edges are golden brown and the cookies are set.
Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.