Wash cauliflower and cut into small sprigs. Slice thick stalks into thin strips.
Heat oil in a wok and add mustard seeds. When mustard seeds start popping add garlic, ginger, turmeric and kalonji seeds. Stir for 1 minute then add cauliflower and walnuts. Toss cauliflower to coat with spices. Add salt and 1/2 cup water. Cover and cook on a medium heat for 5-10 minutes. Uncover and increase heat to evaporate remaining water. Do not overcook cauliflower. Serve.