1. Preheat the oven to 350 degrees F.
  2. Make the vinaigrette: To a small bowl, add the finely chopped shallots and white wine vinegar. Let the shallots sit in the vinegar for 5 minutes to soften. Whisk in the Dijon mustard, kosher, and pepper. Slowly stream in the olive oil, whisking while you pour. Whisk for another minute until emulsified.
  3. Place the walnuts on a rimmed baking sheet, and roast for 12-15 minutes until golden, toasted, and fragrant. Set them aside and let cool.
  4. Assemble the salad: In a large serving bowl, layer in the arugula, sliced ripe pears, and red onion. Top the salad generously with the roasted walnuts, and the crumbled Cashel Blue cheese.
  5. Drizzle the vinaigrette generously on top, and serve immediately.