Step 1: Press the extra-firm tofu for at least 30 minutes (up to an hour) to remove excess water. Once pressed, slice the tofu into uniform 1-inch cubes.
Step 2: In a medium bowl, toss the tofu cubes with 1 tablespoon of cornstarch until each piece is lightly and evenly coated.
Step 3: Prepare the glaze by whisking together soy sauce, rice vinegar, maple syrup, minced garlic, grated ginger, and sriracha (if using) in a small bowl. Set aside.
Step 4: Heat 2 tablespoons of vegetable oil in a large non-stick skillet or wok over medium-high heat until shimmering.
Step 5: Add the cornstarch-coated tofu cubes to the hot pan in a single layer, ensuring not to overcrowd. Cook for 5-7 minutes, turning occasionally, until all sides are golden brown and wonderfully crispy. Cook in batches if necessary, adding more oil if needed. Remove crispy tofu from the pan and set aside.
Step 6: If the pan is dry, add another teaspoon of oil. Add the diced bell pepper and chopped onion to the pan. Sauté for 3-5 minutes until they begin to soften but still retain some crunch.
Step 7: Pour the prepared glaze into the pan with the vegetables. Bring to a gentle simmer, stirring constantly, until the sauce thickens slightly and coats the back of a spoon.
Step 8: Return the crispy tofu to the pan and gently toss everything together, ensuring all pieces are evenly coated in the sauce. Cook for another 1-2 minutes until heated through.
Step 9: Remove from heat. Garnish generously with toasted sesame seeds and freshly chopped green onions before serving immediately.