What are some topics for for an undergraduate thesis about Islam?

A thesis is significantly longer and requires more original research than a seminar paper. Even on an undergraduate level, you are expected to research your topic quite thoroughly, show familiarity with existing scholarship, and make some tangible contribution to an ongoing conversation. This means that you should narrow your topic as much as possible.
Some of your choices will depend on your own background and abilities. A political science student might want to compare the voting habits or degrees of cultural integration of Muslims in contemporary Paris and London suburbs. A history major in the United States might compare anti-Semitism and attitudes towards Jewish refugees in the 1930s and 1940s with Islamophobia and attitudes towards Syrian refugees now. A theology major might look at concepts of the afterlife in medieval Islamic and Christian theology.
To write an effective thesis, you should find a narrow topic within your major area of study that you would be interested in researching exhaustively.