Pizza is a carb-heavy food. While it's alright to indulge once in awhile, it's not something you can consume regularly.
However, if you replace the crust with something lower in carbs (there are options - here, here, and here), you can enjoy the tastes without having to worry about your sugar. With the eggplant replacing the crust, you also get a high-fiber boost.
1 medium - large eggplant (a whole eggplant will have somewhere between 20 and 30 carbs)
1/4 cup marinara or pizza sauce (carbs will vary, but normally less than 10)
1 cup shredded mozzarella cheese (normally about 4 grams)
pizza toppings (take those into account when you're adding your carbs)
Preheat your oven to 425 and grease a baking sheet. Slice the eggplant about 1/2 inch thick. I like to slice it vertically, but it doesn't really matter. If you wanted to use this as an appetizer, you could slice horizontally.
Bake your eggplant for 25 minutes.
When it comes out, move it with a spatula to make sure it didn't stick.
Top your eggplant however you like and bake for another 15 - 20 minutes.