So climate in Cape Town is "Subtropical Mediterranean" according to Wikipedia.
As Leila Rich suggests, broad beans are a good winter crop for this climate, which I share. But they are hardly wind resistant.
Cowpea (Vigna unguiculata) is a good productive summer nitrogen fixer. I grew this last summer and it showed good growth with little to no irrigation, despite some over 40 degree weather. They will blow over in the wind but tend to sprawl anyway so this doesn't pose any problem.
Borage is a must-have plant for generating high amounts of biomass, pollination and accumulating Silicon & Potassium[1].
For wind resistant tree legumes you might want to look at acacias. The seed can be harvested by you or poultry[2].
Sunflowers are a must-have in my garden for insects and seed production. Maximilian sunflower is a perennial species which also has edible seeds but I don't think they have been bred to produce as well as the annual kind (yet...).
1.
http://oregonbd.org/Class/accum.htm 2.
http://www.lrrd.org/lrrd21/7/simo21105.htm