Preheat oven to 400°F.
Line a small baking pan with parchment paper; coat with cooking spray.
Toss walnuts with water in a bowl.
Sprinkle with brown sugar, cinnamon and salt; toss to coat.
Transfer to the prepared pan.
Bake until the sugar is melted and the nuts are just starting to brown, 6 to 8 minutes.
Cool in the pan until the sugar hardens, about 10 minutes.
Mash garlic and salt into a paste in a mortar and pestle or with the side of a knife on a cutting board.
Transfer to a large bowl and whisk in oil, mustard, vinegar and pepper.
Add arugula, pears and the walnuts; toss to coat.