Preheat oven to 425°F. Line 2 baking sheets with parchment paper. Place naan on prepared baking sheets. Evenly spread sour cream mixture on naan, leaving 1/2-inch border. Top with leek mixture, salmon and Swiss cheese. Bake until edges of naan are lightly browned and salmon is cooked through, 10 to 12 minutes. Sprinkle with dill fronds, if desired.