Rinse and drain the tofu. Cut into two-inch squares about an inch thick. For best results, lay on a stack of paper towels to remove the excess water.
Meanwhile, prepare the herbs and seasonings. Mix together the lemongrass, chili, garlic, salt, sugar and pepper. Gently rub the mixture on all surfaces of the tofu squares, taking care not to break the delicate curd.
Using a very sharp pointed knife, cut a cross on one side of the tofu, the cut deeper where the two slashes intersect. Push the remaining spice mixture into the the center of each tofu square.
Heat the cooking oil in a non-stick frying pan. Fry the tofu squares until browned, flipping them over for even cooking.
Arrange the fried tofu squares on a plate. Garnish with sliced scallions. Serve hot.