Preheat oven to 375°F. Line a baking sheet with parchment paper.
Pat salmon fillets dry with paper towels. Season lightly with salt and pepper, then place skin-side down on the prepared baking sheet.
In a small bowl, whisk together olive oil, mustard, honey, lemon juice, garlic, and lemon zest until smooth. Brush about two-thirds of the glaze over the salmon, reserving the rest.
Finely chop the pistachios. A food processor or blender works well, but only pulse briefly. You can also crush them using a bag and meat mallet.
Stir the chopped pistachios into the remaining glaze. Spoon the mixture evenly over each fillet and gently press it onto the salmon.
Bake for 14–18 minutes, depending on thickness. The salmon should flake easily with a fork and reach an internal temperature of 140–145°F.
Let rest for a 2-5 minutes. Sprinkle with parsley if using and serve warm.