Cook the rice according to the package directions.
Adjust an oven rack to the middle position and heat broiler.
Mix the hoisin sauce and 1 tablespoon water in a small bowl. Place the fish, skin-side down, on a foil-lined baking pan and spread the sauce over the top.
Toss the asparagus, mushrooms, oil, 1/4 teaspoon salt, and 1/4 teaspoon pepper in a medium bowl. Scatter the vegetables evenly around the fish. Broil, stirring the vegetables once, until they are tender and the fish is cooked through and opaque, 6 to 8 minutes, depending on thickness.
Slide a spatula between the skin and the fish.
Divide the fish among individual plates, discarding the skin. Serve with the vegetables and rice.