Begin by thoroughly draining the tofu and patting it dry with paper towels. Cut the tofu into 1-inch cubes. Heat 1-2 tablespoons of oil in a non-stick pan over medium-high heat (180°C/350°F). Gently place the tofu cubes in the hot oil and fry until golden brown, about 3-4 minutes per side. Once browned, transfer the tofu to a plate and set aside.
While the tofu is frying, prepare your sauce by combining soy sauce, oyster sauce, Chinese cooking wine, sugar, black pepper powder, and salt in a small bowl. Mix well and set aside.
Using the same pan, add another tablespoon of oil if needed. Add the eggplant cubes and cook over medium heat (165°C/330°F) for 3-5 minutes, stirring occasionally until they become soft in the center. You'll know they're done when a fork easily pierces through.
Push the cooked eggplant to one side of the pan. In the empty space, add a little more oil if needed, then add your chopped onions and minced garlic. Sauté until you can smell the garlic, about 1-2 minutes. Add the chopped red bell pepper and cook until slightly soft but still crisp, about 2-3 minutes.
Return the fried tofu to the pan with the vegetables. Pour your prepared sauce over everything. Using a gentle touch so you don't break the tofu, carefully toss all ingredients together until well combined. Let everything simmer together for 1-2 minutes until the sauce thickens slightly and coats all ingredients evenly.
Give it a taste and add more salt if needed. Once you're happy with the seasoning, remove from heat and serve hot with steamed rice. For best presentation, garnish with chopped green onions if desired.