Mahatma Gandhi is a major figure of not just the 20th century but all of modern history. Students need to know about his life and ideas and will definitely get inspired. A wonderful topic for an ELL / ELT lesson.
Here is a nice series of worksheets you can use for reading, comprehension and understanding of Gandhi's ideas and life.
Also, students can research and fill in the timeline template as a project.
The ppt gives a full overview of his life and times.
Students can read the excellent book on Gif Lingua to get context/background.