Preheat oven to 375 degrees. Cut spaghetti squash in half length-wise and scoop out seeds. Rub cut sides with 1 tsp olive oil and season with half of the Italian seasoning.
Put spaghetti squash halves on a baking sheet, cut side up. Bake for 40-45 minutes or until flesh flakes away easily with a fork.
Heat remaining olive oil over medium-high heat in a large pan. Add onions and sauté until fragrant. Add turkey and break apart with a wooden spoon. Add remaining Italian seasoning and continue cooking and breaking apart.
Once turkey is almost cooked through, add crushed tomatoes and tomato sauce. Lower heat and simmer for 20 minutes, then stir in baby spinach until wilted.