Spray or coat the bottom of a baking dish with oil.

Slice eggplant into coins, about 3/4 inch thick. Grill over medium heat, turning over occasionally to prevent scorching. This takes about 10 minutes.

Remove the eggplant to the baking pan and drizzle evenly with olive oil. Allow the eggplant to sit and absorb the oil, about 15 minutes.

Cover the eggplant slices with marinara sauce. Sprinkle half of the Parmesan over the sauce. Layer the mozzarella on top of the sauce, then finish with the remaining Parmesan. Liberally sprinkle with oregano.

Bake at 350°F for 30-45 minutes, or until cheese begins to turn golden and bubble.

Remove pan from oven and let cool for about 10 minutes before serving.