How to Make It
Preheat oven to 450°F. Peel beets, and cut into 1/2-inch wedges. Place in a small baking dish; cover and bake until tender, 25 to 30 minutes.
Stir together pistachios, mustard, and lemon zest in a small bowl. Place salmon on a baking sheet lined with aluminum foil, and sprinkle with 1/2 teaspoon salt and 1/2 teaspoon pepper. Spoon pistachio mixture on top of salmon; pat into an even layer. Bake at 450°F until a thermometer inserted in thickest portion registers 130°F, 15 to 16 minutes.
Whisk together oil, lemon juice, remaining 3/8 teaspoon salt, and remaining 1/4 teaspoon pepper in a large bowl; reserve 3 tablespoons of the dressing. Add beets, kale-spinach mix, and onion to bowl with dressing, and toss to coat. Transfer to a platter. Place salmon fillet on salad. Drizzle with reserved 3 tablespoons dressing.