Combine cumin and coriander with 2 tablespoons water in a small bowl. Add sugar salt, ginger, and green chilli. Add oil and mix well. Combine cauliflower, potatoes, and tomatoes in a large bowl. Pour the spice mixture over the vegetables and mix thoroughly.
Heat the water in a non-stick skillet at least 25 centimeters / 10 inches in diameter. As soon as it comes to a boil, add bay leaf and the vegetable mixture. You do not need to stir it. Simmer, tightly covered, until the potatoes are tender and cauliflower is still slightly crunchy, 15-20 minutes. Garnish with fresh coriander and serve.