Wrap tofu in a clean kitchen towel and place on a rimmed baking sheet. Weigh down with a heavy object (a couple of heavy cans works well) and let sit 10 minutes.

Unwrap tofu and slice in half lengthwise, then cut crosswise into 6 sections to create 12 squares.

Whisk soy sauce, mirin, sesame oil, gochugaru, and 3 Tbsp. water in a small bowl to combine; set sauce aside.

Trim dark green top from scallion and thinly slice; set aside. Thinly slice remaining white and pale green parts of scallion.

Heat 1 Tbsp. grapeseed oil in a nonstick skillet over medium-high. Carefully add tofu in a single layer and lightly season with salt. Cook, undisturbed, until golden brown, about 5 minutes; turn over and cook until golden brown on other side, about 5 minutes.

Transfer tofu to a plate; reserve skillet (no need to wipe out).

Heat remaining 1 Tbsp. grapeseed oil in reserved skillet over medium. Cook scallion white and pale green parts, garlic, and ginger, stirring, until softened but not browned, about 1 minute.

Return tofu to skillet. Pour in reserved sauce and bring to a simmer. Reduce heat to medium-low and cook, turning tofu once or twice and occasionally spooning sauce over, until sauce is reduced by about half, about 4 minutes.

Transfer tofu to a large plate, spoon sauce over, and sprinkle with sesame seeds and reserved scallion top. Serve with rice alongside.