Heat a medium saucepan over medium heat. Add in onion, garlic and butter. Cook until onions are translucent, about 3 to 5 minutes.
Add in butternut squash and season with salt and pepper. Cook for an additional 2 minutes, then stir in wine. Cook for 1 minute until alcohol dissipates, then pour in water. Reduce heat to a simmer and cook for 10 to 15 minutes until squash is tender.
Add in milk and sage, making sure not to boil (milk will separate if too hot). Season Pacific cod with salt and pepper, then lower into chowder to poach for 5 minutes.
Turn off heat, then gently flake fish into large chunks. Stir in cream, then season to taste. Drizzle on olive oil to garnish. Enjoy immediately.