Add the chicken and broth to a large saucepan and bring to a boil. Remove from the heat. In a medium bowl whisk the eggs and lemon juice together until frothy. Slowly whisk 2 cups of hot stock into the egg mixture - don't just dump it in or you'll end up with scrambled eggs! Once the stock has been incorporated into the egg mixture, add back to the pot. Stir in the spaghetti squash and gently reheat the soup if necessary - don't bring to a boil or the eggs may curdle. Season with salt and pepper. Serve hot, garnished with chopped parsley and grated parmesan cheese (optional).