- 2 small shallots, finely chopped
- 1 large clove garlic, finely chopped
- 3 tablespoons olive oil
- 2 1/2 pounds plum tomatoes, chopped
- 6 stalks fresh lemongrass, tough outer layers removed and lower 6 inches coarsely chopped
- 3/4 teaspoon salt
- 1/2 teaspoon black pepper
- 6 (6 ounce) (1-inch-thick) pieces halibut steak with skin
- Cook shallots and garlic in 1 tablespoon oil in a 3- to 4-quart heavy saucepan over moderately low heat, stirring occasionally, until softened, about 3 minutes. Add tomatoes, lemongrass, salt, and pepper and bring to a boil, stirring. Reduce heat and cook at a bare simmer, stirring occasionally, until tomatoes fall apart and form a chunky sauce, about 20 minutes.
- Force sauce through a medium-mesh sieve into a bowl, pressing hard on and then discarding solids. Season with salt and pepper.
- Prepare grill for cooking. If using a charcoal grill, open vents on bottom of grill, then light charcoal. Charcoal fire is medium-hot when you can hold your hand 5 inches above rack for 3 to 4 seconds. If using a gas grill, preheat burners on high, covered, 10 minutes, then reduce heat to moderate.
- Brush fish on both sides with remaining 2 tablespoons oil, then season with salt and pepper. Grill fish, covered only if using gas grill, on lightly oiled rack, turning over once, until just cooked through, 7 to 8 minutes total. Serve fish with sauce.