Place the poblanos directly on a gas burner on medium-high heat and char the outside skin until black. If you have an electric stove top, place the peppers on a baking sheet and roast on the top rack under the broiler. Rotate the peppers quarter turns until the entire outside is roasted and well-charred. Be careful not to let the poblanos catch fire. Once charred, place both chilies in a small paper bag and seal tightly to allow the peppers to steam and loosen their skins. Set aside. Once cool, remove the skins, remove seeds, dice the peppers and set aside.
In a stock pot over medium heat, add the oil and let it warm. Add the onion to the pan, along with a generous pinch of salt, and sauté. Cook for two minutes or until soft. Add the remaining ingredients, except the cilantro and yogurt. Cook uncovered over medium heat until vegetables are soft, about 30 minutes.
Add the cilantro and carefully puree the soup in several places with an immersion blender. Do not puree until smooth, just purée in with the immersion blender to create a thicker soup base. If you don’t have an immersion blender, carefully transfer half the soup to a blender and purée, and then return it to the soup pot.
Serve chowder topped with a tablespoon of yogurt and a dash of hot sauce if you’d like.