When we were in Lisbon, we once had lunch in a very small sidewalk cafe (two tables) on top of one of the hills that the city is built on. It was in the middle of a residential neighbourhood, few cars but lots of pedestrians, including a whole crowd of five-year-old schoolgirls in cute aprons. It was nice to have something to look at, because the cafe people took their time making this (or something like this; I reverse-engineered it), but it was well worth it!
Heat plenty of olive oil in a thick-bottomed pan. Fry the onion until it starts to colour. Add the garlic and the meat and stir until you don't see any raw spots. Add the lemon juice and if there doesn't seem to be enough liquid to stew in, some stock or water.
Stew for about 45 minutes or until the meat is tender. Stir occasionally.
Add the slices of lemon and salt to taste and heat through for another 5 minutes or so. Serve with rice or bread.