Combine the pea protein and water together in a high speed blender, blend until the water and protein has dissolved. Alternatively, try heating the water and protein up until it dissolves. If the water and pea protein liquid is still in a bowl, add it back into the blender.
Add the pure maple syrup, mustard, onion powder, salt, apple cider vinegar and lemon juice. Blend on full speed until everything has come together and dissolved.
Start adding a little oil at a time (split into 8-10 times) and blend. Be sure you don’t do it too much if you’re using a high speed blender like Vitamix as it may overheat, and if so, you’ll find that it almost becomes a soup with the oil and liquid separate.
Keep blending in small segments and stopping for a minute or so to allow the liquid to cool, until all the oil is used up. By then, the mixture should have thickened quite a bit.
Pour the mayo into a glass container and seal the lid, then refrigerate for a few hours to allow it to thicken further.