Preheat your oven to 350ºF and prepare a 9×13" baking dish with nonstick cooking spray.
In a large skillet over medium-high heat, season the Italian sausage or ground meat with garlic salt and pepper. If using onion, add it as well, cooking until the meat is browned.
Drain excess fat, then stir in marinara sauce and allow to simmer for 15 minutes.
Meanwhile, boil salted water in a large pot, add dry ziti pasta, and cook until just under al dente, about 8 minutes. Drain and toss with a small amount of olive oil.
In the prepared baking dish, layer half of the ziti pasta, followed by half of the meat and sauce mixture. Add provolone cheese slices, dollop sour cream, and repeat with remaining ziti, sauce, and finish with mozzarella cheese on top.
Bake for 30 minutes or until bubbly and golden brown. Let sit for 10 minutes before serving, garnish with fresh parsley if desired.