Remove the tofu from the packet and wrap it in kitchen paper to remove any excess moisture. You may need to press under a weight depending on the producer.
Mix together the gochujang paste, soy sauce, water, cornstarch and sesame oil and set aside.
Top and tail the onion, then peel off the skin before cutting it in half and slicing it into 5-7mm thick slices from top to bottom.
Peel the garlic cloves and slice them as finely as you can.
Slice the spring onions 3mm thick at a 45° angle to the main shaft.
Cut the tofu into slices 1cm (½") thick and 2½cm (1") in profile.
Heat the wok over a high heat, and when it is hot, add the cooking oil. Season the sliced tofu with salt and pepper and add to the wok.
Fry the tofu for 5-6 minutes, flipping over halfway through, being careful not to break it up.Once the tofu is golden, remove it and set it aside on some kitchen paper.
Return the wok to the heat and add the onion and stir-fry for 2-3 minutes.
Add the garlic and cook for 60 seconds.
Return the tofu and pour in the gochujang sauce from step 2, and cook for 5 minutes over a medium heat.