Slow Poached Halibut with Lemon Relish

INGREDIENTS

2 lemons
1/2 small red onion, very thinly sliced into rings
1 teaspoon kosher salt plus more
1/2 cup Kalamata Olives, coarsely chopped
2 tablespoons drained capers, chopped
1 1/4 cups olive oil, divided
Kosher salt, freshly ground pepper
2 pounds halibut fillet
1/4 teaspoons crushed red pepper flakes
1/4 cup fresh flat-leaf parsley leaves

DIRECTIONS

1. Make relish at least 1 hour before the meal.
2. Combine onion and 1 teaspoon salt in a small bowl. Let sit 10 minutes.
3. While the onion marinates in salt,  finely grate zest from lemons in a bowl and set aside. 
4. Using a sharp knife, cut peel and white pith from lemons; discard. 
5. Working over a medium bowl, cut between membranes to release segments into bowl and squeeze membranes to release juices; discard membranes and any seeds. Set lemon segments aside.
6. Squeeze onion to remove any excess liquid; add to bowl with lemon segments.
7. Add olives, capers, reserved lemon zest, and 3/4 cup oil; season with salt and pepper and toss to combine. Cover relish and chill at least 1 hour.
8. Preheat oven to 250°F. Bring relish to room temperature.
9. Place fish in a large shallow baking dish or roasting pan and drizzle with remaining 1/2 cup oil. Add pepper flakes and turn fish to coat; season with salt. 
10. Roast until just cooked through, 30–40 minutes. Transfer fish to a platter. 
11. Mix parsley into relish and spoon over fish.

Source : Epicurious