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.
A chef's salad can include any combination of meat, vegetables and cheese. You can substitute lean roast beef or turkey for some or all of the chicken and ham and include more salad vegetables, such as sliced cucumber and radishes, to the mix. In place of goat's milk cheese, try crumbled fetta or cubes of Swiss-style or havarti cheese.