Heat a large skillet over medium heat. Add 2 tablespoons oil then add in the chicken. Stir fry for 3-5 minutes or until no pink is showing.
Add in the leeks, pepper, and broccoli and cook for 3-4 minutes. Sprinkle with salt and pepper.
Add the ginger and garlic and cook for about 2 minutes.
Stir in the hoisin, soy sauce, beef stock, and vinegar. Cook for one minute then transfer to a bowl.
Add in the remaining tablespoon of oil and add the lettuce. Stir fry for 1 minute or until just wilted.
Add in the sesame oil and salt and pepper. Stir and remove from heat.
Place the wilted lettuce on 4 plates and top with the chicken and vegetable mixture.