Melt the butter in a saucepan and over low heat stir in the spices. Allow them to heat, stirring often, for a few minutes. Stir in the garbanzo beans and enough of the reserved liquid to just barely cover them. Stir well, and mash a few of the beans with a fork or potato masher. Cook over a medium flame for about 20 minutes, or until the sauce is quite thick, stirring often. Remove from heat. Stir in the lemon juice and the diced tomato. Taste, and correct the seasoning.