Bring a large pot of water to a boil over high.

Prepare the sauce: In a small bowl, stir together the peanut butter, brown sugar and vinegar with 1 tablespoon of the soy sauce and half the garlic; season to taste with salt and set aside. (The peanut butter mixture will turn into a thick paste.)

Heat a large cast-iron or heavy-bottomed skillet over low heat until it is hot, 1 to 2 minutes. Add 3 tablespoons of the oil and raise the heat to medium-high. With your hands, crumble the tofu into the pan in a single layer. Let the tofu cook, undisturbed, for about 5 minutes. The tofu that is touching the pan should be golden brown. With a spatula, turn and flip the tofu crumbles and cook, undisturbed, for another 5 minutes.

Add the remaining 1 tablespoon vegetable oil, 1 tablespoon soy sauce, the remaining garlic, the scallions and gochugaru and toss to coat. Lower the heat to medium and cook, stirring occasionally, until the scallions are softened, about 1 minute. Turn the heat off and set the pan aside.

Season the boiling water generously with salt and cook the pasta according to package instructions, 9 to 10 minutes. Drain the pasta, reserve 1 cup of the pasta water, and return the cooked pasta back into the pot. Add the reserved peanut butter mixture and about ¾ cup of the pasta cooking water. Turn the heat on to low and stir the pasta with the sauce until the peanut sauce starts to melt and emulsify with the pasta cooking water and coats the pasta. If the pasta sauce seems too thick, add another splash of pasta cooking water to thin it out.

Divide the peanut noodles between two bowls; top with the tofu crumbles and chopped cilantro.