Chart reviews are as they sound: studies that involve reviewing patients' medical records for information that you need to answer your hypotheses.
Another type of study that is relatively fast to complete is database-based project using either large national databases like the NIS or smaller institution based repositories. Or, if you have the time, you can compile your own databases using your institution's own medical records. Either way, you will need to be statistically savvy for this type of projects, or have available the help of a statistician. Hopefully, your attending can help you brainstorm for ideas, and interpret statistical analysis results.