Cut tomatoes into bite-sized pieces. Trim the root of the shimeji mushrooms and separate them into smaller clusters. Mince the garlic after removing its core.

Heat olive oil and garlic in a pan over low heat until fragrant. Add tomatoes and shimeji mushrooms, stir-fry over medium heat for about 1 minute, then add dried basil and mix briefly.

Add clams to the pan, cover with a lid, and steam over medium heat until the clams open. Once all clams are open, reduce to very low heat and steam for 1 more minute.