Wash and remove the stalk of the cauliflower. Set it on a kitchen towel for all the water to drain. See footnotes on further prep for the cauliflower.
Into the blender add all the ingredients for the marinade.
Blend them into a smooth paste.
Place the cleaned cauliflower on the baking dish and add the quartered onions on the side.
Now pour half the marinade on top of the cauliflower.
Flip over and cover the base of the cauliflower with the marinade as well.
Flip over back and cover the dish with a foil.
Place this on the middle rack of the oven. Place a dish of water at the lower rack and bake for 30 minutes.
Remove the foil, sprinkle the hemp seeds and oregano and bake again for another 20 minutes.
Remove from the oven. Check the doneness of the cauliflower with a fork which passes easily through it.
The dish is now ready to serve.
Notes
Prepping the Cauliflower:since the cauliflower is bunched up it is possible that they may carry some caterpillars inside the florets. To avoid this choose a cauliflower with separated florets so you can see as much as possible. After washing and removing the excess leaves and cutting of the additional stalk, pour some hot water on the cauliflower and rinse again. Alternatively, dunk the cauliflower head in salted water that is on a rolling boil and leave it in for 5 minutes. Drain carefully, this should remove most caterpillars hiding in them.Now I have omitted this step as I don't see any of the caterpillars in the cauliflowers here.