I don't know the specific dish name information, so I can't determine the name of that dish. However, you can try to find this dish in the following ways:

Ask the staff in the school canteen: describe the characteristics of this dish to the staff in the canteen, such as white mushroom slices and other ingredients, and they may be able to tell you the name of this dish.

Check on the school menu or bulletin board: some schools will list the names and prices of dishes on the menu or bulletin board in the canteen. You can check this information to find this dish.

Ask other students: If you know other students who eat in the canteen of Cao Xian Technical School, you can ask them if they know the name of this dish.