Pre-heat a baking sheet in your oven to 375F.
First slice your eggplant starting at the stem end, into thick circular slices. Not to thick where the eggplant wont cook and not too thin where you lose all of your structural pizza integrity.
Soak your eggplant slices in some salt water ( if you have time).
Dice your mushroom into long thin slices and saute with some butter and salt. Once they are about 75% cooked, pull them off and use them to top your pizzas.
Brush all sides of the eggplant with some olive oil, until it can't absorb any more. Place the eggplants on your baking sheet in the oven. Bake in the oven for 10-15 minutes, so the eggplant gets almost 75% cooked. You don't want it soft. Pull it out of the oven
Now top your pizza, first sauce, then cheese, and finally the mushrooms.
Place your eggplant back in the oven, and allow the cheese to melt properly. Pull it out of the oven once the cheese has melted completely.
Let it cool, don't get pizza mouth and melt half your face off.
Enjoy!