based on ur post u have the links from each spok to the hub
on the hub the concentrator creat another l2l tunnel make the rource as the spok 1 and istenation spok 2 this one direction
and vice versa for other direction
then u need to play with :
Configuration > Policy Management > Traffic Management > Rules
make inbound outbound forward rules as required
and apply it to the public interface
good luck
if helpful rate