Preheat the oven to 350°F. Lightly grease an 8x8" baking dish with oil spray. Set aside.
Coat the bottom of the prepared baking dish with 1/3 cup heavy cream. Place 1 layer of parsnips, shingled and slightly overlapping in the bottom of the baking dish. Sprinkle in 1/4 cup sliced green onions, 1/3 cup Parmesan and a 1/4 teaspoon black pepper.