Step 1

Preheat oven to 350 degrees F.

Step 2

Heat olive oil in a frying pan on medium heat. Add onions and garlic and sauté for 5 minutes.

Step 3

Add the tomatoes, lemon juice, rosemary, mustard, salt and pepper. Sauté for 5 more minutes. Remove from heat.

Step 4

Place the halibut steaks in one layer on a lightly oiled baking dish. Cover with rosemary mixture.

Step 5

Cover baking dish with foil and bake for 30 minutes or until fish is cooked through and flaky.