Preheat the oven to 425°F / 220ºc. Place the cauliflower and sliced radish in a large bowl. Add the oil and rub lightly to coat.
Pulse the fennel, mustard, nigella seeds, pepper flakes and salt to a coarse mixture in a spice grinder or blender. Add them to the vegetables and toss well. Spread the vegetables on a parchment-lined baking sheet.
Bake for 25 minutes or until the cauliflower is golden and tender to your preference.
Garnish liberally with cilantro and lemon juice before serving.
Notes
Variation: Use cumin seeds instead of fennel seedsNutritional values based on one serving