If you can use command line on Cisco, why the same scares you on Mikrotik? You can easily translate the command line hierarchy of items to the GUI hierarchy, it is at most places 1:1.
add remote-address=the.cisco.ip.address keepalive=5s,4 name=gre-to-cisco disabled=yes
/interface list member
add list=all-gre interface=gre-to-cisco
/ip firewall filter
set [find chain~"input" action~"drop" connection-state~"invalid"] protocol=!gre
add chain=forward in-interface-list=all-gre prototol=gre out-interface-list=WAN action=accept
You have to place the second rule to the proper place among other rules in the firewall filter (somewhere right after the action=accept connection-state=established,related,untracked one if you use the default firewall). If you want a more precise suggestion, you have to post the export of your current configuration.
If the GRE tunnel doesn't come up, disable it for more than 10 minutes at both the Mikrotik and the Cisco, and then enable it again.
Instead of writing novels, post /export hide-sensitive. Use find&replace in your favourite text editor to systematically replace all occurrences of each public IP address potentially identifying you by a distinctive pattern such as my.public.ip.1.