In a large skillet, heat the oil, two turns of the pan, over high heat. Add the chicken and cook, breaking it up with a spoon and stirring often until lightly browned, about 5 minutes.
Add the leeks, chilies, ginger and garlic; season with pepper. Stir-fry until the leeks are tender, about 3 minutes. Add the hoisin, soy sauce, peanut butter and vinegar. Stir until the sauce coats the chicken, 1-2 minutes. Add the Sriracha (add more if you want more heat) and mix in the peanuts. Serve immediately with lettuce leaves for wrapping.