Can I substitute parmesan or mozzarella for feta in a kale and kabocha squash tart?

Most fetas are saltier than parmesan and a lot saltier than Mozzarella. The texture of mozzarella is Very different from feta when melted. If that is all you have I think that the flavor of parmesan would be a very good substitute.

Neither are ideal substitutions but if those are your only choices I'd go with the parm