In your Openwrt router all you have to do is to edit the dnsmasq.conf file and add a line at the very bottom of the file address=/yourdomain/your_lan_address like this: address=/awesomenetworks.com/192.168.1.121.
Then restart the dnsmasq with /etc/init.d/dnsmasq restart
This will redirect the lan dns requests to awesomenetworks.com to the host 192.168.1.121.
No neet to touch the ISP router.
BTW: The hairpin NAT is widely used in MIkrotik Router OS devices. You may look in Router OS manual if you want to set it up anyway, but it will be not necessary if you set up dnsmasq.conf file and restart the service in your Openwrt router. In other words you either set up Openwrt or the hairpin nat in ISP router. There is no need to do both at the same time.