Bring a large pot of salted water to boil. Heat oven to 450 degrees
In a large skillet, brown cut up sausage, then add in chopped spinach, herbs, scallion greens with a few pinches of salt and pepper. Cook until greens are wilted. Set aside.
Cook the pasta until 2 minutes shy of al dente; reserve 1 cup pasta cooking water, then drain pasta and set aside. Return the pot to the stove.
Melt the butter in the pot over medium heat. Add the scallion whites, garlic and a pinch of salt and saute until softened, 4 to 5 minutes. Add the cream cheese and cooking water and stir until smooth. Stir in the wilted greens and sausage. Add in half the mozzarella and half the feta and stir until combined. Add in the pasta and stir.
Transfer the pasta to a 9x13-inch baking dish and top with remaining mozzarella and feta. Bake until the sauce is thick and bubbly and the top has browned in spots, 10 to 15 minutes. If you like a crispier top, broil for a few minutes.