In terminal, download th qt5 plugins:
sudo apt-get install qt5-style-plugins
Once installed, set to your environment:
sudo nano /etc/environment
Tab down to a new line and ctrl+shift+v to paste in this line:
Hit ctrl+x to exit, then hit the y key to say "yes" to save, then hit the enter key to save as current configuration. The terminal will revert to normal. Upon next boot or login, qt5 apps on Zorin should be styled with the gtk theme.