Clean the squid, remove the skin, and rub with salt to get rid of any residue. Remove the squid heads and discard the eyes. Finely chop the squid tentacles and mix with the ground pork, soaked shiitake mushrooms, onion, and garlic. Season with 2 teaspoons bouillon powder, 1 teaspoon salt, and 1 teaspoon black pepper.

Mix the filling well, then stuff it back into the squid tubes. Use toothpicks to secure the openings so the filling doesn't come out while frying. Heat oil in a pan and fry the stuffed squid until golden brown.

Turn the squid to brown evenly on all sides. In another pan, sauté garlic in oil until fragrant, then add the tomato sauce and bring to a boil. Season to taste. Cut the fried squid into thirds and add to the sauce. Simmer over medium heat so the squid absorbs the sauce and the filling cooks through. Finally, add sliced onion, green onion, and a sprinkle of black pepper on top.