https://www.vegan.com/omega-3/
I quote:
"Vegans can easily meet their ALA needs by consuming a little ground chia or ground flax seeds every day. These seeds are so rich in ALA that it’s possible to cover your entire day’s needs with just a tablespoon. With chia it’s desirable to grind the seeds for better absorption by the body, and with flax it’s imperative to do so—flax is essentially indigestible unless the seeds are ground up. It’s wise to grind right before eating, since ground seeds quickly go rancid without refrigeration. A mortar and pestle or a cheap spinning-blade
coffee grinder will do the job in seconds. Just don’t use a burr-style coffee grinder, or any grinder that’s not based on a spinning blade, or you’ll ruin your machine!"
Also:
https://www.healthline.com/nutrition/benefits-of-flaxseeds#section2
(not saying I believe all the wonderful claims made about it, but I do use it as a source of ALA)