Start by bringing a medium pot of salted water to a boil. Once boiling, gently simmer the tofu for about 2 minutes, or until thoroughly defrosted if using frozen tofu. Drain the tofu in a colander lined with paper towels to remove excess moisture. Once it has cooled down enough to handle, gently press and pat dry. For frozen tofu, apply firmer pressure to squeeze out additional water.

Next, cut the tofu into bite-sized cubes and place them in a medium bowl. Pour in the soy sauce, sesame oil, and black pepper, and toss until the tofu absorbs the liquids. Afterward, sprinkle the cornstarch over the tofu, ensuring an even coating.

Heat 2 tablespoons of olive oil in a large skillet over medium-high heat. Add the tofu cubes, cooking them until they are golden and crispy on all sides, which should take around 7 to 8 minutes. Season lightly with salt and pepper, then remove the tofu from the skillet and set it aside.

In the same skillet, add the remaining tablespoon of olive oil. Stir in the minced garlic and ginger, cooking them for about 1 minute until fragrant. Toss in the string beans, sliced carrots, broccoli florets, red bell pepper slices, and green onions. Cook the vegetables, stirring occasionally, until they are tender yet still crisp, which should take approximately 8 to 10 minutes. Season with salt and pepper to taste.

In a small bowl, whisk together the soy sauce, sesame oil, water, brown sugar, and cornstarch until well combined. Return the cooked tofu to the skillet, pour the sauce over the tofu and vegetables, and stir everything together. Cook for an additional 2 minutes, or until the sauce has thickened slightly and coats the stir fry evenly.

Serve the tofu stir fry hot, ensuring every bite is packed with flavor.