Cut the tofu into cubes and remove excess moisture.
Finely chop onion, bell pepper, and garlic.
Add cooking oil to a pan and fry the tofu on both sides until golden brown.
Remove the tofu and stir-fry garlic, onion, and bell pepper in the same pan.
Add gochujang, tomato sauce, soy sauce, and oligosaccharide to make the seasoning sauce.
Add the fried tofu and stir-fry evenly with the sauce.
Sprinkle sesame seeds and green onion on top to finish.