Frozen Salmon should be sealed in an airtight container with no visible frost on the salmon or inside the packaging. When you purchase salmon fillets, wash and season them before freezing. The freezing process will only intensify the flavors when the frozen salmon is grilled. You'll also want to keep the skin on the salmon when possible. This will help keep it from curling and flaking during the grilling process.
Remove the frozen salmon from the packaging and rinse any ice crystals or frost from the salmon. Pat it dry with a paper towel and brush it with a coat of olive oil on both sides to prevent the frozen salmon from sticking to the grill. Brush the grill grates with olive oil or spray the grill grates with a nonstick oil.
Prepare your grill. Heat the grill to a medium heat or a temperature 375 degrees Fahrenheit. Let the grill reach the heat temperature before you place the frozen salmon on the grill. Place the salmon skin-side up directly on the grill. Sprinkle a combination of thyme, garlic powder and pepper over the top side of the frozen salmon, if you did not preseason the salmon before freezing it.
Grill the salmon for three to four minutes on each side per ½ inch of salmon thickness. If the thickness is 1 inch, grill the salmon six to eight minutes on each side. Turn the salmon only once during cooking time. Handling the frozen salmon too often will cause it to break and flake. Frozen salmon can be ready to serve in less than 20 minutes.