Place a fry pan over a med/high heat, add 1 tablespoon of oil. Season turkey steaks with salt and pepper and cook for 5 minutes each side until just cooked through. Remove from heat and cool. Cut into 1 cm dice.
Add the pancetta to the hot pan and cook for 1 to 2 minutes each side until crispy, remove from heat and roughly chop.
Place turkey in a large bowl; add nectarine, walnuts, watercress leaves, chives, and mozzarella.
For the dressing, place the oil, vinegar, mustard, salt and pepper in a small bowl, whisk to combine. Pour over the salad and toss the salad to combine well.
Remove leaves from the cos lettuce and place on a platter, divide the salad between the leaves and top with chopped pancetta.