Clean and prepare the seafood such as squid, shrimp, and mussels thoroughly.
Cut the onion, carrot, and green onion into bite-sized pieces.
Heat cooking oil in a pan and stir-fry the seafood.
Add the vegetables and stir-fry together.
Add udon noodles and sauce (such as soy sauce, oyster sauce, etc.) and stir-fry.
Season with pepper and serve on a plate.