Preheat your oven to 425 degrees F. Line a rimmed baking sheet with high-heat-resistant parchment paper and spray it with cooking spray.
Slice the unpeeled eggplant into ½-inch rounds, discarding the ends. Season the eggplant slices with salt, pepper, and garlic powder.
In a shallow bowl, whisk the egg with a tablespoon of water. In another shallow bowl, add the almond meal.
Dip each eggplant round in the egg, then dredge in the almond meal. Arrange the coated eggplant slices on the prepared baking sheet. Spray them with cooking spray.
Bake the eggplant until tender, about 20 minutes per side.
Remove the eggplants from the oven, but keep the oven on. Top each eggplant with marinara sauce, mozzarella, and Parmesan.
Return the baking sheet to the oven. Bake the eggplant until cheese is melted, about 5 more minutes. Garnish with chopped parsley and serve.
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Notes
I don't peel the eggplant. Some people worry that the eggplant skin will give this dish a bitter taste, but I don't detect any bitter aftertaste. And the dish looks so much prettier with the dark-colored eggplant skin! However, if you worry about it, there's no harm in peeling the eggplant.