Serve with cooked whole grains, such as couscous, bulgur, or barley.
Preheat oven to 425 degrees. Using a sharp knife, make a few slashes in skin on both sides of fish. Transfer to a parchment-lined baking sheet. Drizzle fish on both sides with oil; season with salt and pepper. Arrange a few lemon slices in cavity, and tuck the rest underneath fish. Tuck a handful of herbs into cavity; coarsely chop remainder and sprinkle over fish. Roast until fish is opaque and cooked through, 20 to 25 minutes.
To serve, use a thin-bladed knife to cut fillet free from top side of fish. Gently transfer fillet to a cutting board with a spatula. Starting from the tail, slowly lift spine to separate it from bottom fillet. Slice each fillet crosswise into three portions; serve.