Preheat the oven to 250°F. In a bowl, toss the bread with 2 tablespoons of the olive oil and 1/8 teaspoon salt. Arrange the bread in one layer on a rimmed baking sheet and bake for 25 minutes.

In a small pot over medium heat, bring the chicken stock to a simmer and reduce by half, 3 to 4 minutes.

In a small bowl, whisk together the remaining 3 tablespoons oil, the vinegar, mustard, and 1/2 teaspoon salt.

In a serving bowl, whisk together the chicken stock and one-third of the dressing. Add the toasted bread and toss. Add the chicken, arugula, tomatoes, pine nuts, and remaining dressing and toss to coat.

Divide the salad among four dinner plates and serve immediately