Pat the salmon completely dry with paper towels. Lightly coat with avocado oil, then season generously on all sides with the hot honey rub. Refrigerate uncovered 20-30 minutes while the grill comes to temperature.
Set up the charcoal grill for indirect cooking at 275-300°F. Bank the lump charcoal to one side and leave the other empty. Add 1-2 small wood chunks (cherry, apple, or maple) to the coals once they ash over.
Slice the lemon into thick rounds. Arrange the slices on the grate over the indirect side, shaped to fit the salmon. Place the skin-on filet directly on top of the lemons.
Close the lid and smoke 25-40 minutes depending on filet thickness. Pull at 135-140°F internal for tender salmon, or 145°F for fully cooked.
While the salmon smokes, combine the honey, red pepper flakes, hot sauce, and apple cider vinegar in a small saucepan over low heat. Warm gently for 5 minutes, stirring occasionally. Do not boil. Pull off heat and let infuse another 5 minutes.
During the final 5 minutes of cooking, brush the warm hot honey generously over the salmon for the glossy sweet-heat finish.
Remove from the grill and rest 5 minutes. Finish with extra hot honey drizzle, fresh parsley, and a squeeze of lemon. Serve immediately.