Break cauliflower into flowerets. Cut each floweret lengthwise, 1/2 inch thick. Cut potatoes into 1/2 inch dice. Soak cauliflower and potatoes in cold water for 1/2 hour. Drain vegetables and dry in a dish towel.
Heat oil in a large skillet. When oil is hot, scatter in fenugreek, fennel, cumin, and red peppers. Stir quickly and add cauliflower and potatoes. Stir and lower heat to medium. Sprinkle the turmeric, coriander, salt, and pepper over the vegetables and sauté for 8 to 10 minutes. Add 1/4 cup water and cover. Turn heat to very low and steam vegetable 7 to 10 minutes until tender. Sprinkle with garam masala, stir, and serve.