To prepare the halibut...if the filet still has the skin on it, you will need carefully slice off the skin by using a sharp filet knife. Otherwise skip this step, and start by cutting the filet into small bite sized pieces and place into a medium bowl.
Zest two limes and one lemon and add to the halibut. Juice all limes and lemons and add to the bowl and stir well. Cover and place in refrigerator for 15-20 minutes to allow the fish to "cook" in the citrus juice.
Finely dice the tomato and toss in with the halibut. Finely chop the cilantro, green onion (green parts only), and the jalapeño. Stir into the marinated halibut along with the olive oil, salt, and pepper.