How do you turn off NAT in Mikrotik. I want the to ping the LAN from the WAN.
Is it possible.
I believe if you re-set the router, reboot, and then bridge the interfaces you want to use without NAT, otherwise remove the NAT from the firewall. 
How do u bridge them actually?
ok the mt does not come with any nat rules defined from the start you would have had to create them
check your firewall for the rules
/ip firewall nat add chain=srcnat action=masquerade
/ip firewall nat add chain=srcnat
/ip firewall nat add chain=dst-nat
These are all to do with nating and redirection to local ips
If yu want to make a bridge aka dumb switch ports
create the bridge
/interface bridge add name=bridge1 disabled=no
add your interfaces to it for example ether3
/interface bridge port set ether3 bridge=bridge1
what ever interfaces are added to the bridge now talk on layer2 and are bridged together