Adding a rich topping helps seal in the juices as it cooks. Also, it's key not to overcook your salmon. Use an instant-read thermometer, insert it into the thickest area of the salmon, and pull the salmon out of the oven when it reaches 135 degrees. Cover loosely with foil and let rest for 5-10 minutes to allow for some carryover cooking time that will bring the internal temperature up to 145 degrees. Marinating salmon for 30 minutes up to 6 hours before cooking will add flavor along with keeping it moist.