Clean the romanesco and cut into small florets, cut the large ones in half. Peel and dice the tomatoes. Peel the onions and cut into small cubes.
Heat the oil in a pan that fits a lid and allow the onions to become translucent. Then put the tomato cubes on top and the romanesco on top. The big, thick florets at the bottom and the small ones on top. Put the lid on and turn back the temperature. After about five minutes, add salt and a good amount of kaffir lime powder, stir once. Steam with the lid closed until the romanesco has the right firmness for you.
For me this is a main course, it goes well with everything as a side dish.