In a medium saucepan, gently simmer chicken in lightly salted water, uncovered, until cooked, 10 minutes. Drain well.
Divide lettuce leaves evenly among serving plates. Top each serving with ½ cup spinach, mounding it in the centre. Cut chicken lengthways into thin strips. Place chicken, ham, capsicum, tomato and goat's milk cheese on each salad.
Whisk together oil, vinegar, mustard, garlic, tarragon and salt in a small bowl. Serve dressing in a jug with the salad.