Line a rimmed, broiler-safe baking sheet with foil for easy cleanup. Fit the baking sheet with a roasting rack (I use a cooling rack) and spray the rack with avocado oil.
Place an oven rack 6 inches below the heating element (the second rack from the top of the oven) and heat the broiler on high (500°F).
In a shallow bowl, mix the grated parmesan with the salt, black pepper, garlic powder, and cayenne pepper.
Place the melted butter in another shallow bowl.
Rinse the scallops and pat them dry with paper towels. If they have a small, crescent-shaped muscle attached to their side, use your fingers to remove it (it gets tough when cooked).
Dip each scallop in the melted butter, then dredge it in the parmesan mixture, turning to coat.
Place the coated scallops on the prepared roasting rack. Lightly spray them with avocado oil.
Broil the scallops 6 inches from the heating element (not directly below) until the cheese is golden brown and the scallops are cooked through - white and moist in the middle - 6-10 minutes, depending on their size. Serve immediately.
Video
Notes
Omitting the salt reduces the sodium per serving to 986 mg.
Exactly how long to broil will depend on the size of the scallops. Today I used colossal scallops - there were 13 per pound - and they needed 10 minutes under the broiler. Start checking after 6 minutes.
There's no need to turn the scallops, but I rotate the baking sheet midway through cooking.
You can keep the leftovers in the fridge, in an airtight container, for up to 3 days. Reheat them in the microwave, covered, at 50% power. I don't recommend freezing the leftovers.