Begin by pressing the firm tofu to remove excess moisture. Wrap the tofu block in a clean kitchen towel or paper towels and place a heavy object on top for 15-20 minutes. Once pressed, cut the tofu into bite-sized cubes or rectangles.
In a small bowl, combine the Korean red chili powder, pounded red chili (if using), soy sauce, sugar, and water. Stir well until the sugar dissolves completely.
Heat the tablespoon of oil in a non-stick skillet over medium heat. Add the tofu pieces in a single layer and cook without stirring for about 4-5 minutes until the bottoms are golden and crispy. Flip the tofu carefully to brown all sides evenly, about another 4-5 minutes.
Once the tofu is golden on all sides, add the minced garlic and sliced green onions to the pan. Stir gently and cook until the garlic is fragrant, about 1 minute.
Pour the chili paste mixture over the tofu and reduce the heat to low. Let it simmer for 3-4 minutes, allowing the tofu to soak up the sauce and thicken slightly. Stir occasionally to coat every piece with the spicy glaze.
Drizzle the sesame oil over the tofu and sprinkle with toasted white sesame seeds. Give it one last gentle stir, then remove from heat.
Serve your Spicy Korean Tofu hot over steamed rice or alongside your favorite noodle dish.