Combine stem lettuce and pinch of salt in another bowl.
Combine water and cornstarch in a small bowl; stir into a smooth paste.
Transfer half of the cornstarch paste into a larger bowl. Add pork, rice wine, and 1/4 teaspoon salt. Mix well and let marinate, about 5 minutes.
Whisk remaining cornstarch paste, chicken stock, soy sauce, black vinegar, and sugar in another bowl to make sauce.
Heat oil in a wok or large skillet over high heat. Add pork with marinade; cook and stir until browned, 3 to 4 minutes. Stir in pickled chile peppers and chili bean sauce; cook until oil turns red, about 1 minute. Add spring onions, garlic, and ginger; cook and stir until fragrant, about 1 minute. Stir in lettuce; saute until tender, 2 to 3 minutes. Pour in sauce and toss until thickened, about 3 minutes.
