Vegetarian replacement for pork mince in Chinese style stir fry
It seems like you are primarily interested in reproducing the umami of the meat.  Tofu does in fact have glutamic acids that will add to the umami; just make sure to thoroughly dry the tofu (extracting as much liquid as possible) before use.  In addition, you can use minced mushrooms, as Stephie mentioned in the comments.  You can also experiment with adding Bragg's Liquid Aminos, since it has a lot of umami but has less than half the sodium of soy sauce.

Keep in mind, though, that the meat in the original recipe is also relied upon for its fat; tofu does have some fat, but not as much as meat, and it's unlikely to render out during the initial fry.  Therefore, I would suggest adding 7 grams of fat (e.g., vegetable oil) for every 100g of meat you are replacing.