Whisk vinaigrette ingredients in bowl. Store up to a month in the refrigerator.
ROAST: Preheat oven to 400 degrees. Remove the outer leaves of the brussel sprouts and reserve. Halve brussels sprouts and toss in a bowl with cauliflower florets, olive oil, and salt. Roast cauliflower and brussels sprouts on a sheet pan for 30–40 minutes until golden brown, shaking occasionally for even browning.
BLANCH: Meanwhile, blanch brussels sprout leaves in a pot of boiling water for 30 seconds. Immediately cool in an ice bath and pat dry.
COMBINE: Toss brussels sprouts, cauliflower, blanched leaves, citrus, and tofu in a bowl, and dress with 1/4 c. fish sauce vinaigrette.