First, prepare the tofu by removing any excess moisture. If you have a tofu press, use it for 30 to 45 minutes. If you don't, remove the tofu from the package, dry it with paper towels, wrap it in a tea towel, and place something heavy on top of it. Leave it in the refrigerator for 1 or 2 hours.

Once the tofu is drained, cut it into bite-sized pieces and put them in a container with a lid.

In a small bowl, mix dark soy sauce, vinegar, garlic powder, and vegetable oil (if desired) to e a marinade. Pour the marinade over the tofu and stir-coat it well. Cover the container and put it in the refrigerator for 20 minutes.

After 20 minutes, put the tofu and cornstarch in a Ziploc bag and shake it until the tofu is coated with cornstarch.

In a large skillet, add 2 to 3 tablespoons of vegetable oil over medium heat. Once the oil is hot, add the tofu to the pan evenly, being careful to not overcrowd the pan. Cook the tofu for 2 to 3 minutes per side, until golden brown and crispy on all sides. Transfer the tofu to a large bowl.

While the tofu is cooking, prepare the sauce in a small saucepan. Add soy sauce, apple cider vinegar, water, chili sauce, brown sugar, and cornstarch to the pan and whisk to combine. Cook over low heat for 3 to 5 minutes, or until the sauce has heated through and thickened.

Once the tofu and sauce are both done cooking, pour the sauce over the tofu and stir to coat before serving. You can add vegetables to the skillet while cooking for added texture and flavor.