Spread salt level (about 1 in. deep) in a 5- to 6-quart oval or 9- by 13-inch rectangular baking dish. Heat in a 450º regular or convection oven until very hot, about 20 minutes.
Meanwhile, sprinkle one side of halibut lightly with salt and pepper. Pour olive oil into a 10- to 12-inch nonstick frying pan over high heat. When hot, place fish pieces in pan, seasoned side down, without crowding; work in batches if necessary. Cook until lightly browned on the bottom, about 2 minutes.
Remove baking dish from oven and distribute thyme and oregano sprigs, bay leaves, and all but three of the lemon slices evenly over hot salt (some salt will still be visible). Set halibut pieces browned side up over herbs and salt, spacing evenly. Cut reserved lemon slices in half and place half a slice on each piece of fish.
Bake until fish is opaque but still moist- looking in center of thickest part (cut to test), 15 to 20 minutes. Serve with herb oil to drizzle over fish to taste.
Sodium varies in nutritional analysis.