Preheat your Traeger grill to 225°F.
In a bowl, whisk together the maple syrup, soy sauce, Dijon mustard, olive oil, garlic powder, onion powder, black pepper, smoked paprika, and red pepper flakes until well combined.
Place the salmon fillet in a shallow dish or a resealable plastic bag and pour the marinade over it. Ensure the salmon is well coated. Marinate in the refrigerator for at least 30 minutes, or up to 2 hours for more flavor.
Remove the salmon from the marinade and let any excess drip off. Discard the marinade.
Place the salmon skin-side down on the grill grates. Close the lid and smoke for about 1 to 1.5 hours, or until the salmon flakes easily with a fork and reaches an internal temperature of 145°F.
Once cooked, remove the salmon from the grill and let it rest for a few minutes. Serve with fresh lemon wedges and garnish with chopped parsley.