If you're serving this baked pasta on the night you prepare it, preheat the oven to 375 degrees F.
Heat the water to a boil for pasta, salt the water and undercook the pasta by about 2 minutes.
While the water comes to a boil, heat the extra-virgin olive oil in a large skillet over medium to medium-high heat, add the garlic and onions, soften a few minutes then stir in chard to wilt. Then add the scallions, dill, mint, parsley, and black pepper. Reduce the heat to a simmer and keep greens warm.
Meanwhile, heat the butter in a saucepot over medium to medium-high heat. As soon as the butter melts, add the flour and stir 1 minute. Whisk in milk and season with salt, pepper and nutmeg, to taste. Cook 4 to 5 minutes, or until the sauce is thickened.
Drain the pasta and place back in hot pot, stir together with greens and feta to combine, taste to adjust seasoning. Place the pasta in a casserole dish and top with bechamel sauce and Parm cheese, place in oven and bake until bubbly and brown, 20 minutes or, cool and cover then store. To reheat, place in 375 degrees F oven and bake 45 to 60 minutes until brown.
NotesPastitsio is a Greek baked pasta dish traditionally made with ground lamb or beef, often with bits of spiced or cured meat mixed in, this is a healthy Greek alternative to Lasagne Bolognese. Here, I use an equally traditional phyllo tart filling and use it to lighten up the end result, though it remains rich yet not heavy - think a well-made spinach or vegetable lasagna.