Press the firm tofu for about 15 minutes to remove excess water, then tear it gently into bite-size pieces using your fingers.
Peel and mince the garlic and ginger.
Place the torn tofu in a bowl and pour 2 tablespoons soy sauce over it; stir gently to coat and let sit for a couple of minutes, then drain any excess liquid.
Add 2 tablespoons cornstarch to the tofu and toss gently until pieces are evenly coated.
Heat 3 tablespoons vegetable oil in a large skillet over medium-high heat. Fry the tofu pieces in batches, 2–3 minutes per side, until golden and crisp. Transfer to paper towels or a wire rack to drain.
Wipe the pan if needed, then heat the remaining 1 tablespoon vegetable oil over medium heat. Add the minced garlic and ginger and cook, stirring constantly, for 1–2 minutes until fragrant but not burned.
Add the hoisin sauce, 1 teaspoon sriracha, 1 teaspoon cane sugar, the remaining 2 tablespoons soy sauce, and 2 teaspoons sesame oil to the pan. Stir and bring the sauce to a gentle boil.
Add the fried tofu to the sauce and toss gently until all pieces are evenly coated and heated through.
Serve immediately, optionally garnishing with chopped scallions and sesame seeds if desired.
