Cut the squash in half lengthwise. Using a spoon, remove the center seeds and stringy parts of the flesh, discard. Using a roasting pan, pour just enough water to cover the bottom. Place the squash cut-side down and cover with foil, bake 35-45 minutes, or until tender. Squash is done when a fork can easily pierce the flesh.
In the meantime, add ground turkey to a skillet and cook over medium heat, breaking up with a fork. Cook turkey until it’s no longer pink, drain off any fat and add marinara, stir to combine. Remove from heat and cover.
In a separate skillet, heat olive oil over medium-low heat, add garlic and sauté 1 minute. Add spinach and sauté just until wilted, about 3 minutes. Remove from heat and combine salt, pepper, cottage cheese, 1 cup mozzarella, and egg white. Cover and set aside.
Remove tender squash from the oven and allow to cool until it can be handled, drain water from the pan. Use a fork and scrape the inside of the squash to remove the spaghetti type strings. Transfer spaghetti strings to a large mixing bowl. Add the spinach and cheese mixture to the cooked spaghetti squash and stir to combine.
Fill the squash boats with the spaghetti squash cheese mixture, and top with meat sauce. Sprinkle remaining cheese over the meat sauce. Return boats to the roasting pan and bake 15-20 minutes until filling is hot, and cheese is bubbly. Remove from oven and allow to set for 5 to 10 minutes before serving.