Cut chicken into fine strips. Wash and dry spinach leaves, discarding any hard stalks.
Heat 2 Tbsp. of olive oil in a skillet. Stir-fry chicken for several minutes.
Add spinach and cook for about 1 minute, or until barely wilted. Add pine nuts and cook for 1 more minute. Spoon the contents of the pan onto serving plates. Pour the vinegars into the pan with the remaining 1 Tbsp. of oil.
Season with pepper and stir until mixed. Lightly toss with the torn lettuce leaves. Pour over the mixture on the plates and serve immediately. Top as desired.