Halibut is a superfood compared to other fish. It's packed with potassium, protein, vitamin D, B-12, B-6, and magnesium. Plus, its meat is lean, which is ideal for rapid weight loss.
Preheat oven to 400°F. Lightly oil a 9-by-13-inch baking dish; arrange fish in dish. In a small bowl, whisk 1 Tbsp. oil, 1 Tbsp. lemon juice, salt and 1/4 tsp. pepper. Drizzle vinaigrette over fish. Bake until just opaque in center, about 10 minutes.
In a food processor, combine parsley, chives, garlic, scallion, anchovy paste and capers. Add remaining lemon juice and 1 Tbsp. water and pulse until finely chopped. With motor running, add remaining oil. Season sauce with 1/8 tsp. pepper. Spoon sauce over fish just before serving.