Bake the squash: Place a rack in the upper and lower thirds of your oven and preheat the oven to 400 degrees F. Slice the squash in half lengthwise and scoop out the seeds. Drizzle the cut sides with 1/2 teaspoon olive oil each and then sprinkle 1/2 teaspoon salt and 1/4 teaspoon pepper over all. Place the squash cut-side down on a rimmed baking sheet. Pour 1/4 cup of water into each baking sheet to prevent sticking. Bake for 45 to 50 minutes, until the squash flesh is fork-tender and the skin gives a little when pressed. Remove from the oven and set aside to cool.
While the squash is baking, heat the remaining tablespoon oil in a large skillet over medium high. Add the turkey, 1 teaspoon salt, remaining 1/2 teaspoon pepper, Italian seasoning, and red pepper flakes. Stir and cook, breaking apart the meat into small pieces, until it is fully cooked through and browned on all sides, about 4 minutes. Stir in the garlic and cook until fragrant, about 1 minute more. Reduce the heat to low. Stir in the pasta sauce and red wine vinegar. Let simmer 1 minute. Taste and adjust the seasoning as desired.
Place the spinach in a large mixing bowl. Use a fork to separate any large clumps. Add the ricotta, 1/2 cup fontina, and remaining 1/2 teaspoon salt. Stir with the fork to combine. When the squash is cool enough to handle, use a fork to fluff the insides into strands and add the strands to the bowl. With the same fork, stir to combine, evenly distributing the ingredients as best you can. Return the squash halves to the baking sheet, cut sides up.
Brown the top (optional): Turn the oven to broil. Broil the squash until the cheese is extra bubbly and lightly browned, about 2 minutes. Watch it carefully, and do not walk away so that it doesn't burn. Sprinkle with parsley and enjoy!
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