Preheat oven to 350°. In a small skillet, melt butter over medium heat; stir in sugar and pepper. Add walnuts; toss to coat. Spread evenly onto a baking sheet. Bake until lightly browned, about 15 minutes, stirring every 5 minutes. Cool on a wire rack.
Place dressing ingredients in a blender; cover and process until blended. Place salad ingredients in a large bowl; toss with dressing. Top with walnuts. Serve immediately.