Drain tofu from packing liquid. Pat dry with paper towels to absorb moisture. Cut into ½- inch cubes.
Trim about 2 inches from the kangkong stalks and discard. Cut kangkong into 3-inch lengths, separating the sturdier stalks from the leaves. Wash thoroughly and drain well.
In a bowl, combine oyster sauce, chili garlic sauce, water, sesame oil and cornstarch. Stir until well-blended and set aside.
In a wide skillet over medium heat, heat oil until hot. Add tofu and cook until golden and crispy. Remove from pan, drain excess oil on paper towels and keep warm.
Remove excess oil from the pan except for about 2 tablespoons. add onions and cook until softened.
Increase heat to high. Add sauce mixture and cook until bubbly, stirring until thickened.
Add sturdy stalks and cook for about 30 seconds or until half done.
Add kangkong leaves and cook, stirring regularly, for another 30 seconds or until tender yet crisp.
Add tofu and quickly toss until lighted coated with sauce.
Season with salt and pepper to taste. Serve hot.