In a large stockpot (15-quart works well) heat oil over medium-high heat. Add onion, pasilla and poblano peppers. Cook until onions just become translucent, about 3 minutes. Stir in garlic and cook until it becomes soft and fragrant, about 1 minute.
Add beans and enough broth to cover them. Cook until beans are soft, about 20 minutes. Stir in remaining vegetables and season to taste with salt. Allow to simmer until tender, about 15 minutes.
With a handheld immersion blender, do four quick pulses to blend some of the soup and vegetables to make soup a little creamy without additional fat or cream. Add turkey; cook another 5 minutes. Drizzle in vinegar to help balance sweetness; season to taste with sea salt.
Serve stew with fresh herbs (thyme, sage and mint).
Editor’s Note: If you can’t get Mexican squash, you can substitute zuchinni (the younger and sweeter the better). It’s possible that a local tienda has all the Mexican ingredients.