Pack the sliced onions into a heat-proof glass jar. In a small saucepan, combine the water, vinegar, maple syrup and salt. Bring the mixture to a simmer. Carefully pour the hot mixture into the jar over the onions.
Press the onions down with a spoon so they are submerged by the vinegar mixture. Allow to cool. Seal and refrigerate.
For the quinoa:
Rinse quinoa well in a sieve with cold running water. Transfer to a pot with the vegetable stock and bring to the boil. Reduce to a simmer and cook for approximately 20-30 minutes until all the stock has been absorbed. Fluff with a fork and allow to cool.
Steam tender stem broccoli for a few minutes until just tender but still crunchy. Roughly chop and add to a large mixing bowl.
Into the large mixing bowl add the cooled quinoa, cooked spelt, sliced mushrooms, diced avocado, leafy greens and a handful of pickled onions. Toss gently to combine.
Transfer tossed salad into a large bowl and scatter with almonds and pomegranate rubies. Dress with a little olive oil and pickled onion juice just before serving.