To make the sauce, combine all the ingredients in a big bowl. And adjust the flavour according to your preference.
To prepare the silken tofu, cut it into 2.5-4 cm (1-1.5") thick cubes or pieces. Let the tofu remain on a plate to drain excess water.
While waiting, heat a non-stick pan on medium heat and add oil.
Saute the onion and the white parts of the green onion/scallion until they turn translucent. Then add garlic and saute until fragrant.
Add sliced sausages and diced tomatoes, and cook for about 5 minutes or until the tomatoes turn soft.
Add the vegan egg replacement. Continue to cook until it has a scrambled egg consistency, or tofu scramble if using (see notes).
Set aside the sausages, tomatoes and tofu/egg on a small plate.
Using the same pan, add a little oil on medium heat. Toss in the silken tofu and pour the vegan egg/replacement over it.
Cook the tofu for a few minutes before mixing in the tomato and sausage mix.
Pour in the sauce over the sausages, tofu and "egg", cover the pot, and let it cook for 2 minutes or till the sauce thickens.
Stir everything together. Adjust the seasoning to your taste with more veg oyster sauce or soy sauce, if necessary.
Remove from fire. Garnish with the green parts of the green onion/scallion, and serve hot over steamed noodles or rice.