2 tsp. Dijon mustard
2 tbsp. finely chopped shallot
2 tbsp. white-wine vinegar
¼ cup walnut oil or extra-virgin olive oil
1 5-ounce package baby arugula
½ cup very thinly sliced red onion
1 cup red grapes, halved
2 cups cubed cooked chicken ( ½-inch; about 10 ounces)
⅛ tsp. ground pepper plus ¼ teaspoon, divided
¾ tsp. salt, divided
1 tsp. extra-virgin olive oil
2½ cups halved Brussels sprouts (or quartered, if large)
2¾ cups precubed butternut squash