To make the sauce, combine the sweet soy sauce, vegetarian oyster sauce, soybean sauce, and sriracha in a small bowl and set aside.
Heat a wok or large skillet over high heat and add the oil.
When you see the first wisp of white smoke, add the garlic, chilies and tofu.
Cook until the garlic starts to brown, about 30 seconds.
Stir in the onion and bell pepper and stir-fry for about 1 minute.
Add the reserved sauce to the wok and combine the ingredients thoroughly for about 1 minute.
Add the Thai basil leaves and cook until the tofu is thoroughly cooked and the onion is slightly tender.
Finish with the white pepper and serve.