Clean the fish by removing all bones and scales, but leave the skin on. Filet or butterfly into 8 oz portions.
Rinse mackerel filets in cold water.
Mix all the brine ingredients together in a large container. You can use a bowl, bucking, baking dish, or zip-top bag.
Gently place the mackerel filets in the brine and soak them overnight in the fridge for 6-8 hours.
Then, gently remove the mackerel from the brine, and rinse it under cold water again.
Pat the mackerel filets dry with paper towels. Then, let them air dry on a wire rack in the fridge for 1-2 hours.
While the mackerel dries, prepare the glaze and the grill. Mix all of the glaze ingredients together in a microwave-safe bowl.
Preheat your Z Grills pellet smoker to 225°F.
Using a paper towel soaked in oil, grease the grill grates.
Once your pellet smoker is preheated to 225°F, place the mackerel skin side down directly on the grill grates.
Smoke the mackerel for about 30 minutes with the lid closed.
After 30 minutes, apply the glaze with a brush. If the glaze becomes too thick to brush on easily, microwave it for 10 seconds until it thins out.
Every 20-30 minutes, brush another thin layer of glaze on the mackerel.
When the internal temperature of the mackerel reaches 145°F, remove it from the smoker and serve immediately. Your smoked mackerel will take about 2-4 hours total, depending on the size of your mackerel fillets. Watch your thermometer closely!