Preheat the oven to 400. Place a cast iron skillet or other oven-safe skillet over medium heat.
Chop the eggplant into 1/2 inch chunks. Add the olive oil to the pan and add the eggplant to the pan. Stir occasionally to cook evenly.
Whisk the eggs, milk, ricotta and mozzarella in a large bowl. Add the salt and oregano and stir to combine.
After about 10 minutes, the eggplant should be cooked down and soft. Chop the garlic and add to the pan. Stir for one minute to cook.
Add half of the eggs to the pan. Add 1/4 cup of the marinara sauce to the pan and swirl. Add the rest of the eggs and the remaining marinara and swirl to combine. The mixture should resemble a marble cake.
Place in the oven and bake until puffy, about 20 minutes. The top should appear golden brown. Remove from the oven and allow to cool for 10 minutes before serving.