In a medium bowl, soak the tofu in the salt and 2 cups of water for 10 minutes. Make sure all the tofu is submerged. The brine will draw out excess moisture from the tofu, helping it become crispy and flavorful when cooked. Drain the tofu and pat it dry with a paper towel.
In a large bowl, stir together the tapioca starch and white pepper. Add the tofu and gently toss to coat it completely. Let the tofu sit in the mixture for about 5 minutes to ensure the coating sticks.
Heat the canola oil in a large frying pan over medium-high heat. Add the tofu and fry it until crispy and golden brown all over, 7 to 8 minutes, stirring every 30 seconds. Using a spider or slotted spoon, transfer the tofu to a large plate. Pour the oil out of the pan and wipe it clean.
In a small bowl, stir together the garlic, ketchup, rice vinegar, light soy sauce, vegetarian oyster sauce, plum sauce and sugar.
Add the sauce to the pan and simmer it over medium heat until it thickens, for about 2 minutes. Add the crispy fried tofu, increase the heat to high and sauté for about 1 minute, turning to coat with the sauce.
Transfer the tofu to a plate and garnish it with the sesame seeds and scallions. Serve immediately.
