Preheat oven to 500 and with a rack in the middle. Sprinkle olive oil on the baguette slices and toast until lightly browned. Or if you’re like me until you remember you’ve got them in the oven and they’re nicely “charred” on the edges. Set aside.
In a large bowl, combine the chicken, mayo, whole grain mustard, walnuts, grapes, salt, and pepper. Mix to combine. Taste and add more mayo, mustard, salt or pepper as needed.
Top the baguette slices with the chicken salad and garnish with grated Parmesan and chopped chives.