Place the squash, carrot, leek, apple, and broth in a slow cooker or a large pot. If using a slow cooker, cover and cook on high for 5 hours or low for 8 hours. If using a pot, bring to boil then reduce heat to low and simmer, covered, until squash is soft when pierced with fork (about 30 min).Stir the coconut milk into the soup mixture. Puree the soup using an immersion or stand blender.Head a medium nonstick skillet over medium-low heat. Add the oil and leeks and cook, stirring occasionally, until golden and crisp, about 10 minutes. Season with salt.Pour the soup into 6 serving bowls and garnish with crispy leeks. If desired, drizzle with a little coconut milk.