Melt butter in a stockpot over medium heat.
Add onion, poblano, carrot, celery, coriander, cumin, thyme and lightly season with salt & pepper. Stir occasionally until onions become translucent, about 5 minutes.
Sprinkle flour over veggies and stir for about 30 seconds.
Stir in tomato paste and add in the broth and milk. Stir to combine.
Next, add potatoes and corn. Bring to a boil. Cover and reduce to a simmer. Cook, stirring occasionally for about 15 minutes, or until potatoes are tender.
Add in shredded chicken and spinach. Stir and cover, continuing to simmer for about 10 minutes.
Serve warm. Can top with fresh lemon juice, if desired