I am moving a L2L tunnel from an ASA to a Meraki MX100. I understand how to set the tunnel piece up, but in this specific case I need to source NAT the local network to the remote network. Similar to the below.
Hopefully your vendor will go for it. We've got a number of tunnels between our ASAs and client's Meraki MX, where we're doing VPN NAT on the ASA side. MX doesn't care so long as you tell it the correct subnet.