Make the eggpant sauce: warm 2 tbsp of olive oil in a saucepan. Dice the eggplant and add it to the oil. Sauté on medium-high heat for 3 minutes, always moving it around the pan. Lower the heat and add the chopped tomatoes. Add salt and oregano to taste, stir, cover and let simmer on low heat for 20-25 minutes.
Make the pasta: bring a pot of water to the boil, add salt and pasta and cook for about 2/3 of the recommended cooking time indicated on the pasta package. Drain and rinse the half-cooked pasta under cold water to stop the cooking. Set aside.
Make the bechamel sauce: in a smaller saucepan, toast the flour on medium heat for a couple of minutes. Add the butter and whisk to make a roux. When the butter and flour are combined, add the cold milk and stir to dissolve all lumps. Add salt to taste and bring to a boil, then remove from the heat.
Assemble the pasta dish. Combine the cooked pasta and eggplant sauce and spread 1/3 of it on the bottom of a casserole dish. Add 1/3 of the bechamel sauce and a sprinkle of parmesan cheese. Keep working in batches, in order to make sure there is bechamel and parmigiano all over the dish, working in layers. Top with more parmigiano on the top layer.
Bake in the preheated oven at 200°C for 20 minutes, then switch to broil and leave for an additional 10 minutes to nicely finish the top layer.