Drain the tofu and wrap in clean kitchen towels or paper towels. Remove excess water from the tofu by placing a weight on top. Let sit for 10 minutes. Unwrap the tofu and cut it into bite-size pieces.
Season tofu with 2 teaspoons of soy sauce. Sprinkle cornstarch on top, tossing to coat.
Heat 2 tablespoons oil in a large nonstick saute pan over medium heat. Add the tofu and spread in an even layer. Cook until browned, about 3 minutes. Flip and brown on the other side. Remove from heat and set aside.
Combine ingredients for the sauce including chicken or vegetable stock, oyster sauce, soy sauce, fish sauce, and brown sugar in a small bowl. Set aside.
In the same pan, prepare the sauce. Heat the remaining tablespoon of oil over medium heat and add the chopped bell pepper. Saute for 2 minutes or until softened. Add garlic and Thai chili, cooking for 30 seconds or until aromatic.
Add sauce mixture and bring to a boil. Mix cornstarch with water to make a cornstarch slurry and add it to the sauce. Simmer until slightly thickened, stirring constantly. Remove from heat.
Add the tofu and basil to the sauce and toss to evenly coat. Serve immediately with steamed rice.
Notes
You can drain the tofu and let it sit overnight in the fridge until ready to cook.