Satueed spinach with walnuts

Very quick side dish for a busy weeknight! I loved it, Paulo gave it a "so-so" rating, but at least he tried it and ate the walnuts.

1/4 red onion, thinly sliced
3 gloves garlic, sliced
Spinach, washed and stems removed, still damp (this would work with baby spinach as well)
walnuts, about 1/4 cup
olive oil
balsamic vinegar

Heat the olive oil in the pan, about two tablespoons.  Add the red onion and saute until soft.  Add the garlic and cooking until fragrant, add in the walnuts.  Dump in the damp spinach and stir well, put the lid on and walk away for about two minutes.  Come back and sprinkle the whole bunch with balsamic vinegar, serve hot.