How can I get zsh completion to expand environment variables like bash does?

Question

When using bash, if I have an environment variable called SOMEPATH which contains a path (e.g. SOMEPATH=/usr/local/lib), then if I type

ls $SOMEPATH/

and hit tab then bash expands the environment variable so my command line now says

ls /usr/local/lib/

If I do the same thing in zsh it instead escapes the $ sign so after tab completion the command line looks like

ls \$SOMEPATH

How can I get zsh to behave like bash does in this regard?

I've done a lot of googling but I haven't managed to find anything that exactly addresses this issue. I've also tried reading the zsh documentation but again I couldn't find anything that obviously relates to this.

Thanks for any pointers.