In the university main building there is a student cafeteria, Unicafe, which offers a selection of warm meals as well as a salad option. Their menus for the week are available here. (Choose "Päärakennus" from the restaurant list.)
Other Unicafes close by can be found in Porthania (Yliopistonkatu 3) and Metsätalo (Fabianinkatu 39).
Other lunch options in the vicinity are for example the following: