Blend the flaxseeds and water in a high speed blender until all flaxseeds are well processed and set aside until an egg white consistency appears (about 5 minutes).

Meanwhile blend together the soy milk, dates, mustard seeds, onion powder, salt, vinegar and lemon juice in a blender until a smooth consistency appears and no dates are detectable anymore.

Then add the flax seed mixture into it and keep blending until just combined.

Now begin adding the oil. With the blender running, use the hole at the top to put in a tablespoon at a time blending for about 30 seconds after each addition.

Keep doing that until the whole oil is incorporated and the mayo takes on a thick consistency.

Transfer to a glass container with a lid and refrigerate for few hours. It will thicken even more and the taste will change slightly over time. It keeps in the fridge for about a week.