In a small bowl, combine the sugar, salt, and one teaspoon piment d'Espelette.
Sprinkle the cure over the salmon, spreading it around to coat the filet.
Refrigerate for 5 hours.
Rinse the salmon and pat it well with a paper towel to dry.
Heat a smoker to 400 F.
Place the salmon on a roasting rack and place the rack in the smoker. Smoke until the internal temperature reaches 145 F (or your desired doneness), about 20 minutes.
Meanwhile, combine the herbs, shallot, garlic, olive oil, and remaining 1 teaspoon piment d'Espelette in a small bowl.
Zest the lemon into the bowl and stir to combine.
Remove the salmon from the smoker and place it on a large serving dish.
Drizzle with the salsa verde and sprinkle with lemon juice, if desired.