Preheat oven to 425°F. Prepare four parchment hearts.
In a small dish, combine hoisin sauce, soy sauce, vinegar, Sriracha (if using), honey, and ginger.
Arrange a layer of orange slices, then bok choy over one half of each piece of paper. Place salmon on top; season with salt and pepper. Divide sauce over salmon; seal packages.
Arrange packets on two large baking sheets. Bake 10 minutes, switching position of pans halfway through. Transfer packets to plates with a wide spatula. Slit tops; gently open. Finish with sesame seeds and scallions. Serve with rice.