Heat the oven: Up to 425°F (220°C) degrees.
Roasted eggplant: Transfer the eggplant slices to paper towel and wipe them with as much water as possible. Also dry the baking sheet, coat it with 3 tablespoons of olive oil and sprinkle the oil with several black peppercorns. Arrange the eggplant slices in a single layer. Drizzle with 2 more tablespoons of oil and ground black pepper. Roast until bottom is golden brown, 20 to 25 minutes. Use a thin spatula to flip the eggplant slices and roast until golden brown on the second side, another 10 minutes. It’s okay if they’re not cooked yet. Reduce oven temperature to 375°F (175°C).
Meanwhile, prepare the sauce: While the eggplants are roasting, open your can of tomatoes and use kitchen scissors or very well-washed scissors to cut the tomatoes into small pieces. Heat 2 tbsp of olive oil in a medium/large saucepan over medium-high heat. Once hot, add the onion and cook until softened, about 8 minutes. Add garlic and chili flakes and cook for another minute. Add the tomatoes (watch out for splashing!), oregano and season with 1 tsp salt, plus more to taste. Simmer the mixture over low heat for about 10 minutes, stirring occasionally. If you want a smoother sauce than it currently is, you can crush the tomatoes more with a potato masher while cooking, or use an immersion blender for a completely smooth sauce. Stir in the basil then taste the sauce; Adjust salt and pepper to taste.
To assemble: In a 1.5 to 2 liter baking dish (holds 6 to 8 cups; I use This), pour in about 1/2 cup of sauce. Arrange about half the eggplant slices, slightly overlapping, in a single layer. Pour in another 1/2 cup of sauce and spread it evenly. Arrange the remaining eggplant slices, then pour more sauce over them to make it as flavorful as you want. (Store unused sauce in refrigerator another day; it will keep 4-5 days.) Sprinkle top with mozzarella and Parmesan.
Cook: For 30 minutes, until the cheese is melted and the sauce is bubbling all over. For more color on top, you can briefly put it under the broiler of your oven.
Serve: Once cooked, let the eggplant parmesan sit at room temperature, if you can, for 15 minutes before digging it in – this helps the ingredients settle and come together more. It’s not mandatory, but it’s great with a side of garlic bread.
Do it in advance: Eggplant Parmesan keeps well in the refrigerator for up to 5 days. Reheat in the oven at 350 degrees, covered for the first half of the time, for about 25 to 30 minutes. You can also freeze it, well wrapped, for a few months.