Preheat oven to 450°. Put cauliflower on a rimmed baking sheet, drizzle with 2 tablespoons oil, sprinkle with 1/2 teaspoon salt and 1 1/2 teaspoons cumin, and toss to coat evenly; then spread in a single layer. Roast, 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 cauliflower is roasting, make dressing: In a small bowl, whisk together lemon juice, honey, remaining 1/4 teaspoon salt and 1/4 teaspoon cumin, and pepper. Whisk in the remaining 3 tablespoons olive oil.

In a serving bowl, combine roasted cauliflower, mizuna, and dates, drizzle with dressing, and toss to coat evenly. Taste and add additional salt and pepper if needed. Serve immediately.