Combined handful of fresh chives dill, oregano and parsley sprigs, roughly chopped plus more for garnish
Preheat the oven to 325 degrees F. Line a rimmed baking sheet large enough to hold the salmon with parchment. (The parchment will make it easier to transfer the salmon in one piece from the baking sheet to a serving plate.)
Drizzle 2 tablespoons of the oil on the parchment. Scatter the onions and toss with oil on the pan. Top with half of the citrus slices.
Place the salmon skin-side down on the onions and citrus. Using a very sharp knife, slice the salmon crosswise 3 to 5 times into serving portions, leaving about 1/4 inch intact at the bottom attached to the skin. This will make it easier to serve the salmon at the table.
Arrange the remaining citrus slices around the salmon. Drizzle the remaining 2 tablespoons oil over the citrus and salmon, including in between the scored portions. Season with salt and pepper. Top with the handful of herbs, pressing them into the salmon to coat with a little bit of the oil.
Roast the salmon until barely cooked through, 20 to 40 minutes, depending on the thickness of the salmon. To check the salmon, poke the center with the tip of a sharp paring knife and twist it. Start checking at 20 minutes, then every few minutes after until the center is just opaque .
Using the parchment, transfer the salmon, onions, and citrus to a serving platter. Garnish with more fresh herbs.
To store leftovers, remove the citrus and discard, then refrigerate the salmon in an airtight container for up to 2 days.