Why fry onions without oil and then add oil?
According to Wikipedia,


  the preparation of a wat begins with chopped onions slow cooked, without any fat or oil, in a dry skillet or pot until much of their moisture has been driven away. Fat (usually niter kibbeh) is then added, often in quantities that might seem excessive by modern Western standards, and the onions and other aromatics are sautéed before the addition of other ingredients. This method causes the onions to break down and thicken the stew.