Preheat your Traeger smoker to 225°F (107°C).
Pat the salmon fillets dry and season with salt, pepper, and garlic powder.
Place the salmon fillets on the smoker, skin side down, and smoke for 1 to 1.5 hours until the internal temperature reaches 145°F (63°C).
While the salmon smokes, combine the softened butter, lemon juice, lemon zest, and chopped dill in a small bowl. Mix until smooth.
Remove the smoked salmon from the smoker and immediately spread the lemon-dill butter on top.
Serve the salmon hot, garnished with lemon slices and dill sprigs.