Heat vegetable oil in a skillet over medium heat. Add tofu in a single layer; cook until golden brown and easily released from the bottom of the skillet, about 3 minutes. Flip and continue cooking until golden brown on the second side, about 3 minutes more.
Mix soy sauce, green onions, water, sesame seeds, sesame oil, red pepper powder, and black pepper together in a small bowl. Spread over the cooked tofu. Garnish with red pepper flakes.