Turkey Sausage-Stuffed Acorn Squash

Ingredients

• 3 acorn squash (about 1½ lb/750 g each)
• 1 tsp canola oil or olive oil
• 1 small onion (diced)
• 1 rib celery (diced)
• 1 small apple (peeled and diced)
• 1 lb turkey sausage (casings removed)
• 2 tbsp fresh sage (chopped)
• ½ tsp salt
• ½ tsp pepper
• 1 cup whole wheat croutons
• ¾ cup Parmesan cheese (grated)
• ⅔ cup walnuts (coarsely chopped (optional))