Hi @johnpoz
I have NAT enabled on both pfSense firewalls, however as a test I disabled NAT to ensure all natting was handled by the Cisco router and I was still unable to reach the 10.0.20.10 client.
RFC1918 blocking is disabled on all the pfSense interfaces.
I can access all clients on the LAN network of the pfSense LAB with NAT enabled. I also have a static route on the Cisco router for 10.0.15.0/24 via 10.0.50.10 and I can access any host on that network with no issues.
After some more playing around today I got it working.
Firstly I had to assignin the ovpns1 interface and enable it under the Interfaces > Interface Assignments.
Then I was required to add the 10.0.100.0/24 network into the “IPv4 Local network(s)” under the OpenVPN Tunnel Settings, however this setting wouldn't apply until a reboot of the pfSense.
Thanks to everyone for the suggestions.
Tyler