If i've understood well,
You got a client (wireless connection)
You want it to connecto to YOU on your wireless interface
Link your wireless interface to your wired interface
and your wired interface connected on your router ?
##Client## ---- Wireless ---- ##Wlan0 -> Computer -> Eth0## ---- Wired ---- ##Router##
If it is, then what i should have done is :
Setting up a Fake Ap (it will use Wlan0 as a fake access point, and eth0 to get access to the internet)
Since datas go through wlan0 and eth0, no need of MITm with ettercap, because it's a MITM in itself.
Let's just capture packets with wireshark, apply filters if you want to see only your client's packets, and i think u're done.
I hope u'll understand my answer (i'm french T-T), anyway, if i've misunderstood something, or if i've not been clear enough PM me