How to Make It
Gently toss together tofu and 1/4 teaspoon of the salt in a bowl. Spread tofu in an even layer on a kitchen towel or double layer of paper towels; let drain 10 to 15 minutes. Meanwhile, stir together 3 tablespoons water, Bragg Liquid Aminos, sugar, garlic, sesame oil, cornstarch, pepper, and remaining 1/8 teaspoon salt in a small bowl until sugar dissolves; set aside.
Heat canola oil in a large nonstick skillet over medium-high until shimmering. Pat tofu with paper towels to remove excess moisture. Add tofu to hot skillet; cook, stirring occasionally, until browned on 2 to 3 sides, 5 to 6 minutes.
Whisk together 2 tablespoons water, vinegar, sugar, salt, and pepper in a large bowl. Add onion; top with watercress, mint, and tomatoes (if using). Do not toss salad; set aside.
Reduce heat under tofu in skillet to medium; pour Bragg Liquid Aminos mixture over tofu. Cook, stirring often, until sauce reduces slightly and clings to tofu, 1 to 2 minutes. Remove from heat.
Toss together salad ingredients in bowl; transfer to a serving dish. Top with tofu; spoon remaining sauce in skillet over tofu.