Mix garlic, yellow bean sauce, and Shaoxing rice wine in a bowl.
Add the pork to the bowl and stir to coat.
Mix all sauce marinade ingredients in a separate bowl and add to the pork.
Cover the bowl with cling film and refrigerate for at least 24 hours.
Heat groundnut oil in a wok until smoking.
Stir-fry the pork for 4 minutes until browned, reserving the marinade.
Add the reserved marinade and boil.
Simmer for 4 minutes until the sauce becomes thick and sticky.
Heat oil in a small pan and stir-fry red onions for 5 minutes.
Add vinegar and sugar, cooking for 3 minutes until caramelised.
Fill grilled buns with salad, pork slices, onions, and tomatoes.