Preheat oven to 350 degrees F (175 degrees C). Grease a baking dish with cooking spray.

Heat oil in a skillet over medium heat; stir in turkey sausage and spinach. Cook and stir until sausage is browned and spinach is wilted, about 5 minutes.

Combine egg whites and almond milk in a large bowl; stir well. Add sage, thyme, oregano, red pepper flakes, basil, nutmeg, salt, and pepper.

Layer grated sweet potatoes evenly on the bottom of the baking dish. Add turkey and spinach on top. Pour egg mixture over casserole. Sprinkle Parmesan cheese on top.

Bake in the preheated oven until bubbly and the top is golden brown, about 45 minutes. Cut into 6 pieces.