Clean king oyster mushrooms and squid thoroughly, then cut them into bite-sized pieces.
Slice onion, bell pepper, and other additional vegetables into bite-sized pieces as well.
Heat cooking oil in a pan, then stir-fry the king oyster mushrooms and squid first.
Add the vegetables and stir-fry together.
Mix in gochujang (Korean chili paste), soy sauce, minced garlic, sugar, pepper, and other seasonings.
Once the ingredients are cooked through and well seasoned, turn off the heat and transfer to a plate.