Preheat oven to 400°F (200°C).
Toss butternut squash cubes with olive oil, half the salt, and half the pepper on a parchment-lined sheet pan.
Roast squash for 22 minutes or until fork-tender and slightly caramelized.
In a large skillet over medium-high heat, sauté the diced onion and minced garlic until translucent, then add ground turkey and cook until browned and fully cooked through.
In a high-speed blender, combine the cottage cheese, egg whites, dried sage, nutmeg, and remaining salt and pepper; process until completely smooth.
In a large mixing bowl, fold together the roasted squash, cooked turkey, and chopped baby spinach.
Transfer the mixture into a 9x13 inch baking dish and pour the blended cottage cheese sauce evenly over the surface.
Top with grated Parmesan cheese and bake at 375°F (190°C) for 20-25 minutes until the protein binder is set and the cheese is golden.
Allow the dish to rest for 10 minutes to firm up before slicing into four equal servings.