Combine first 10 ingredients in a small bowl. Place the salmon in a shallow, nonstick or parchment paper-lined baking dish. Spoon mixture in bowl over salmon; season with salt and pepper. Let salmon marinate 10 minutes.
Preheat oven to 425°F. Place cauliflower in a medium pot and cover with 2" cold water. Bring to a gentle simmer and cook cauliflower until quite tender, about 12 minutes. Meanwhile, bake salmon 12 to 15 minutes, or until cooked through.
When cauliflower is tender, drain well and thoroughly mash. Mix in butter, milk and nutmeg; season with salt and pepper.
To serve, mound mashed cauliflower in the centre of each of 4 plates. Set a piece of salmon on top of the cauliflower on each plate. Spoon over pan juices, sprinkle with parsley, and serve.