Multifunctional guild plant for central Mexico

Hi, folks! A few months ago I visited a friend in central Mexico (Aguascalientes), and his wife asked me to give her some tips on what to plant in their back yard. Like a lot of back yards in that country, it has a 12' high concrete wall at the back and 8' walls on either side. The back wall is on the north side, so the yard acts as a suntrap and gets quite hot. The soil is not sandy per se, but quite dry and low in organic matter. So far they're growing cactus and succulents in pots.

I recommended citrus for the two back corners, and she was pleased with that suggestion, but she was confused when I recommended goumi for the understory. I looked it up and sure enough, goumi does not grow that close to the tropics. I'm wondering what other multifunctional plants I should recommend instead. I tried to join the online community for permaculture in Mexico, but it keeps telling me my password doesn't match. So I turn to you... what would you suggest? Thank you in advance.

What about Feijoa aka Pineapple Guava?