Cut the tofu into bite-sized pieces.
Slice the onion and green onion.
Heat cooking oil in a pan and fry the tofu on both sides until golden brown.
Push the fried tofu to one side of the pan and stir-fry the onions and green onion.
Mix gochujang, soy sauce, sugar, and minced garlic to make the sauce.
Add the sauce to the pan and stir-fry until both tofu and vegetables are well coated.
Sprinkle with sesame seeds at the end to finish.