If you prefer your liver well cooked, cook for a few minutes longer but this toughens it and reduces the iron content in the recipe. Remember, liver continues to cook even after you remove it from the stove. So one other option is to place the cooked liver in a sealed container so that it cooks further but remains tender.
You can also serve this recipe over any plain steamed grains like rice, couscous or with polenta, all will compliment this dish really well.