Preheat the oven to 450°F. Put the cauliflower on a rimmed baking sheet, drizzle with 2 tablespoons of the oil, sprinkle with 1/2 teaspoon of the salt and 1 1/2 teaspoons of the cumin, and toss to coat evenly, then spread in a single layer. Roast the cauliflower, stirring once or twice, for about 15 minutes, until golden brown and tender but not mushy. Taste a floret for doneness; larger florets may take slightly longer to cook.
While the cauliflower is roasting, make the dressing: In a small bowl, whisk together the lemon juice, honey, the remaining 1/4 teaspoon salt and 1/4 teaspoon cumin, and the pepper. Whisk in the remaining 3 tablespoons olive oil.
In a serving bowl, combine the roasted cauliflower, mizuna, and dates, drizzle with the dressing, and toss to coat evenly. Taste and add additional salt and pepper if needed. Serve immediately.
Reprinted with permission from Brassicas by Laura B. Russell (Ten Speed Press, © 2014). Photo credit: Sang An.