Wrap the beets in tin foil with the stem side up, leaving the cut stem exposed to the air. Place in a baking dish and roast for 90 minutes.
Allow the beets to cool enough that they can be safely handled then cut into wedges. Combine with the rest of the purée ingredients in a blender or food processor and blend until very smooth. Cover and let stand in the refrigerator.
Make the topping: melt the butter of medium high heat in a medium sized skillet. Add the red onion and minced ginger and stir gently until they start to loosen and release fragrance but before they turn translucent. Pull from heat and set aside. Stir in the walnuts.
Combine all ingredients for the salad in a large bowl and toss to even distribute.
To plate: spoon the purée onto serving plater or divide between plates. Use the back of the spoon to push the purée around and "paint" the surface almost to the edge. Pile the salad on top then sprinkle the topping over it. Garnish with edible flowers like bachelor buttons and marigolds.