Cut tofu into small cubes. Place on paper towels, sprinkle with salt, and let sit while you prepare the rest.
In a bowl, mix mayonnaise, soy sauce, vinegar, oyster sauce, and water. Set aside.
Sprinkle cornstarch over the tofu and toss until lightly coated.
Fry tofu in a single layer over medium-high heat until golden and crispy. Drain on paper towels, then pour out excess oil.
In the same pan, sauté onion and garlic until softened. Add chilies and cook for about a minute.
Add tofu and sauce, then toss with the aromatics. Turn off the heat right away so the mayo doesn’t separate.
Season with pepper. Top with onions, scallions, fried garlic or shallots, and calamansi or lemon, if you like.