In Spain if your lunch is composed of sandwitches for a quick one, in some places of south Spain you can get a lunch for two for $12.

Also, on some Chinese Woks I could get a box of rice with chicken and some vegetables+addons such as onion rings for 12-13 euros. The box is pretty big so it can be split nicely without feeling yourself half-empty afterwards.

This probably doesn't qualify for "taking my wife out to lunch".

A few years back in Lisbon I got a simple main dish for 3€ in a restaurant. That was surprisingly cheap, I guess this is not possible in Spain, also not in the cheapest regions.

Possible in Extremadura, Andalusia and the Castilles. Also, Spain has the concept of "menú del día", a complete cheap menu. That's it: a starter, a second dish and a dessert. In the South of Spain you can find cheapish prices from 6 eur to 10.