For this salad, arugula makes a fine substitute for spinach, if desired.
Place spinach, oranges, dates, and olives in a large salad bowl; set aside. In a small bowl, whisk together orange juice concentrate, vinegar, and mustard; set aside. In a large nonstick skillet over medium-high heat, saute chicken in oil for about 3 minutes. Add garlic and saute for 2 minutes more. Stir in juice concentrate mixture and cook about 3 minutes. Season with salt and pepper. Spoon warm chicken mixture over salad and gently toss to mix. Portion salad onto dinner plates and top with crumbled goat cheese.