Clean the bean sprouts and thinly sliced pork belly thoroughly.
Add cooking oil to a pan and stir-fry the pork belly first.
When the pork belly is about halfway cooked, add the bean sprouts.
Season with salt and pepper.
Stir-fry quickly over high heat until the bean sprouts soften.
Transfer to a plate and, if desired, sprinkle with chopped scallions or sesame seeds.