Preheat the oven to 400°. Liberally coat a baking sheet with oil spray.
Slice the eggplant into rounds (about 10 slices). Arrange the eggplant slices in a single layer on the baking sheet. Mist the tops of the eggplant slices liberally with oil spray, and lightly sprinkle with kosher salt and pepper (omit the salt if you have high blood pressure). Bake for 20 minutes, or until eggplant is soft and golden brown.
Top each slice with about 1 tablespoon marinara sauce and 1 heaping tablespoon mozzarella cheese. Sprinkle the slices with the grated cheese, as well as oregano and crushed red pepper to taste. Bake for another 5 to 10 minutes, or until the cheese is hot and bubbly.