To prepare dressing, place a colander in a 2-quart glass measure or medium bowl. Line colander with 4 layers of cheesecloth, allowing cheesecloth to extend over sides. Spoon yogurt into colander. Cover loosely with plastic wrap; refrigerate 12 hours. Spoon yogurt cheese into a bowl; discard liquid. Combine yogurt cheese, 1 1/2 tablespoons water, mustard, vinegar, and garlic; stir well. Set dressing aside.
Preheat oven to 350°.
To prepare croutons, arrange bread cubes in a single layer on a jelly-roll pan. Lightly coat bread cubes with cooking spray. Sprinkle evenly with 1/4 teaspoon Italian Spice Blend, 1/8 teaspoon pepper, and dash of salt; toss well to coat. Bake at 350° for 15 minutes or until lightly browned; set aside.
To prepare chicken, heat a large nonstick skillet over medium-high heat. Rub chicken with 1 teaspoon Italian Spice Blend, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Coat skillet with cooking spray. Place chicken in pan; cook 4 minutes on each side or until done. Remove chicken from pan; cool slightly. Cut chicken across grain into thin slices.
To assemble salad, combine croutons, romaine lettuce, and watercress in a large bowl. Drizzle with dressing; toss well to coat. Place 2 cups salad on each of 4 plates. Divide the sliced chicken evenly among salads, and sprinkle each serving with 1 tablespoon grated Parmesan cheese. Sprinkle with additional freshly ground black pepper, if desired.