Make the relish: Preheat the oven to 350 degrees F. Spread 1/2 cup walnuts on a baking sheet and bake until toasted, 7 to 10 minutes. Let cool, then finely chop and transfer to a bowl. Add a pinch of cayenne pepper, 1 tbsp fresh lemon juice, 1 tsp honey, 2 tbsp diced roasted red pepper, 1 tbsp walnut oil, 1 tbsp olive oil and 2 tbsp parsley. Add 1/2 tsp salt and black pepper to taste and toss to combine. (The relish can be made up to 1 day ahead; cover and refrigerate.) Make the salmon: Raise the oven temperature to 425 degrees F. Combine 1 tbsp olive oil and 2 tbsp parsley, 2 tbsp chopped fresh chives, 1 tsp grated lemon zest, 1/2 tsp salt, and black pepper to taste in a bowl. Rub the herb mixture all over the 2 -to-3-pound piece salmon. Lay skin-side down in a baking dish and roast until just cooked through, 12 to 14 minutes. Let rest 5 minutes, then transfer to a platter and top with the walnut-pepper relish.