Place water, lemon juice and olive oil in a saucepan and heat to boiling. Add rice, cover tightly and reduce heat to lowest setting. Simmer for 50 minutes without lifting the lid.
When the rice has cooked for 40 minutes, prepare halibut. Chop onions, place in a saucepan with dried tarragon and sauté in butter or margarine over medium heat for 2 minutes. Add halibut steak to onions, sprinkle with pepper and pour undrained tomatoes over the top. Cover and reduce heat to medium-low.
Crush then mince garlic and add to halibut. Chop cilantro.
When rice has cooked for 50 minutes, remove lid and fluff with a fork. Add chopped cilantro and replace lid. Simmer for 5 to 10 more minutes or until all the moisture has been absorbed and serve with tomato-smothered halibut.