Prep the tofu. Start by pressing the tofu in a tofu press or weigh it down with heavy objects for 15-30 minutes. Pat it dry. Slice it lengthwise in half through the long edge and into 6 small tofu planks (see video or step-by-step pictures).
Marinade the tofu. Whisk the soy sauce, water, lime juice, and sugar in a rectangular baking dish. Arrange the tofu planks in a single layer and flip them a few times until covered in marinade. Place in the refrigerator to rest for a minimum of 30 minutes or preferably overnight.
Cook the tofu. Heat a skillet or grill pan with a little oil. Once it's very hot, add the tofu planks and cook for 2-3 minutes on each side over medium-high heat. Save the marinade. Reduce heat to medium-low and cook the tofu for another 5-7 minutes per side until crispy.
Make the sauce. Mince the shallot and the green part of the green onion very thinly. Wash the mint and cilantro and remove the thick stems. Chop them very finely. Combine everything with the rest of the marinade and red pepper flakes.
Serve. Pour the sauce over the tofu and serve right away.
Notes
Serving size: You can use 14 ounces (400 g) of tofu for 2 if serving it as a main course. If it's part of a larger meal, 14 ounces can be sufficient for 4 people.
Don't use sweet or low-sodium soy sauce.
Make a double batch of marinade and sauce, if you like it saucy.