Dry the tofu and cut into cubes. I wrap the tofu in towels and place a plate on top of it until excess liquid is absorbed by the towels. You can also opt to use a tofu press.
In a shallow plate or bowl, mix the cornstarch and salt. Coat the tofu well in the mix.
In a bowl, mix all the ingredients for the sauce and set aside.
In a pan, heat around 2 tbsp of oil and then fry the tofu cubes until crisp and golden. You will need to turn around the tofu cubes to evenly crisp them.
Take out the tofu and set aside. In the same pan, sauté the onion in a little sesame oil, if using.
Mix the sauce again to make sure the cornstarch hasn’t stuck to the bottom. Add in the sauce and orange slices (if using) to the pan then mix well. Leave to simmer over medium heat while mixing. The sauce will slowly thicken from the corn starch. Add in the tofu and coat in the sauce. Leave to cook for 2-3 minutes.
Serve with a bowl of rice and enjoy while hot!