There are two options for cooking the eggplant:: either in the oven or on coals in an outdoor grill. If you are using the oven, preheat it to around 400 Fahrenheit and place the eggplants on a baking sheet. bake until very soft and custard like in the middle. If you are using the outdoor grill method (I prefer this method) place the eggplants directly on the coals. Leave them there, turning occasionally, until they are soft and the skin begins to split slightly.
When the eggplants are done, remove them from the coals/oven and allow them to cool off a little. Once they are cool enough to handle, peel off the skin with your fingers (be careful! the first time I tried this I was impatient and got a really bad blister because they were so hot!). The skin can sometimes be a little tricky to get off, especially if you use the grill. Don't worry too much about getting all of the skin off, but you do want to get rid of most of it.
In a blender, puree the beans (rinsed, of course!). Add the eggplant and puree until smooth. Add the flavorings. Pour in all of the lemon first, then add the oil and tahini until you get the right consistency. You should not need much oil or tahini - this dip should already be pretty moist and rich. Taste and adjust your spices. Get creative with your seasonings!
Serve with pita or fresh veggies! My favorite way to serve this dip is in a pita with some grilled portabella mushrooms. (yummmm!) Enjoy!