Preheat the oven to 425 degrees.
Place sweet potatoes and onions on a sheet pan; drizzle with oil, sprinkle with salt. Roast in the oven for 30-45 minutes, until golden brown and softened.
At the same time, place the cauliflower florets on a second sheet pan, toss with 1 tablespoon oil and 1 teaspoon salt. Roast in the oven for 30 minutes.
Break up the cauliflower into smaller bits using the back of a wooden spoon or spatula. Return to the oven for 10-15 minutes to get extra browned.
Allow the sweet potatoes and onions to cool slightly. Working in two batches, transfer the sweet potatoes and onions to a blender. Add broth, ginger, and macadamia nuts; puree until very smooth.
Taste and adjust for salt. Serve the soup topped with the roasted cauliflower bits, a sprinkle of chives, a drizzle of oil, and a squeeze of lemon juice.
