How to Make It
Heat a grill pan over medium-high heat. Sprinkle salmon with 1/4 teaspoon salt and 1/4 teaspoon pepper. Coat pan with cooking spray. Place salmon, skin side down, in pan; cook 5 minutes. Turn and cook 3 minutes for medium-rare or until desired degree of doneness.
Place 1/2 teaspoon salt, remaining 1/4 teaspoon pepper, 1/4 cup walnuts, 2 1/2 tablespoons oil, juice, and avocado in a food processor. Pulse until almost smooth.
Place remaining 1/4 teaspoon salt, arugula, and radishes in a large bowl. Add remaining 1 1/2 teaspoons oil; toss. Divide salad among 4 plates. Top with salmon and guacamole. Chop remaining walnuts, and sprinkle over the top.