When z is aliased to cd the <space><Tab> doesn't invoke zi

[bwinterfp]

I have cd aliased to z ie. alias cd:'z' in my .zshrc. When I try cd some-path<space<Tab> zi is not called, whereas if I type z some-path<space<Tab> I get the interactive list. How do I keep cd but also have access to oxides interactive zi without having to type z xxx<space><Tab>?