Heat the vegetable oil in a large skillet or wok over medium-high heat.
Cut the pressed tofu into bite-sized cubes and add it to the skillet. Cook until golden brown on all sides, about 5-7 minutes. Remove the tofu from the skillet and set aside.
In the same skillet, add the onion and garlic. Sauté for 1-2 minutes until fragrant.
Add the sliced bell pepper and green beans to the skillet. Stir-fry for about 3-4 minutes until the vegetables are tender-crisp.
Return the tofu to the skillet. Add the soy sauce, oyster sauce, and brown sugar. Stir well to combine and cook for an additional 2-3 minutes.
Remove the skillet from heat and fold in the fresh Thai basil leaves until just wilted.
Serve the stir-fry over cooked jasmine rice.