Preheat the oven to 350ºF and line a baking sheet with parchment paper. (You'll need to bake 2 batches or use 2 baking sheets to bake all of this dough at once.)
In a large bowl, stir together the ground flax or chia seeds and water. Let this rest in the bowl for 5 minutes to create the vegan "egg."
Add in the almond butter, coconut sugar, salt, baking soda, and vanilla, and stir well to create a thick dough. Add in the vinegar and stir again. Fold in the oats and chocolate chips.
Use a heaping tablespoon to scoop the dough onto the lined baking sheet. It's okay if the cookie dough feels a little oily-- that can happen from over-mixing the dough, but the cookies still turn out well. Use your hands to flatten and shape the cookies, as they will only spread out slightly.
Bake at 350ºF for 10 to 12 minutes, until the cookies have spread out a bit and look lightly golden. They will still be soft to the touch, so let them cool on the pan for at least 10 minutes before removing them with a spatula. Enjoy warm, or cool completely on a wire rack.
These cookies can be stored at room temperature for several days, but they will dry out if left uncovered. Grain-free cookies tend to get softer if stored in an airtight container, so for best texture I recommend storing them in the fridge or freezer if you won't be serving them all right away.