The -T option extracts the named section from the input file. By default, all loadable sections are extracted from the input file. You can specify multiple -T options on the command line to extract more than one section.
hex app.hzx -Ftxt -TIDATA0 -TCODE
This reads the application file app.hzx, extracts the sections IDATA0 and CODE (ignoring all others) and writes them to the file app.hzx.txt.