place cut cauliflower in saucepan with water and 1/2 tsp salt. cover and simmer till cauliflower is crisp-tender, about 10 minute set aside and cover to keep warm.
heat small skillet over low heat and roast cumin seeds until dark and fragrant. remove cumin from pan and set aside to cool. add coriander seeds to pan and slowly roast them till dark brown. do not burn spices. when coriander seeds have cooled, use clean coffee grinder to grind them with the cumin seeds and set aside.
heat oil in large saucepan and add ginger, garlic, and turmeric. stir constantly over medium heat until mixture turns golden brown. this will happen quickly, so be careful not to burn it. crush tomatoes with hands and add them to pan along with juices. when tomatoes come to a boil, stir in chile, cayenne, cumin, coriander, and remaining 1/2 tsp salt. lower heat and simmer sauce about 8 minutes or till tomatoes are well cooked. the oil will start to separate from sauce. add cilantro and simmer 1-2 more minutes.
place warm cauliflower on platter, pour sauce over it, and serve dish immediately.