Preheat oven to 425. Line a baking sheet with nonstick foil.
Make crust; pulse walnuts, breadcrumbs, lemon zest, oil, salt and pepper in a food processors until crumbly.
Place salmon filets, skinned side down, on baking sheet; brush tops with mustard. Press crust evenly onto filets. Bake until just opaque in center, about 15 minutes.
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