No. You cannot (even if is physically possible to do it via LuCI). Your firewall will not work properly or predictably if you attempt this.
Each network must be assigned to at most one firewall zone (typically it would be exaclty one, but you can actually leave a network unassociated with a firewall zone). You can allow or deny intra-zone forarding, allow zone > zone forwardings (or deny them by not explicitly allowing them), and/or you can make more granular rules at the network or host level by IP addresses/subnets.