Preheat the broiler. Rub the poblano pepper with the vegetable oil. Place on a baking sheet and put it in the oven as close as you can to the broiler without touching. Broil for 10 minutes on each side or until the skin of the pepper blisters and starts to turn black. Remove the pepper from the oven and place into a bowl and cover with plastic wrap. Once the pepper is cool enough to handle, peel the skin off and remove the stem and seeds. Finely chop the pepper and set aside. (You can do this part in advance)
Meanwhile, heat a large, heavy pot over medium heat and cook the bacon until crisp. Drain the bacon onto paper towels and reserve 2 tablespoons of the fat in the pan. Add the onions to the pan, cooking until onions are soft and beginning to brown, about 5 minutes.
Stir in the garlic and oregano and cook for an additional minute. Stir in the potatoes and the chopped poblano pepper and then pour in the chicken stock and salt. Bring the stock to a simmer, cover and cook until potatoes are tender, about 10 minutes.
Add in the bacon, pepper, corn and all but ¼ cup of the milk and bring to a simmer. Whisk the remaining milk and the flour together until smooth and then slowly whisk into the pot. Cook for another minute or two until the soup thickens, check for seasoning adding more salt or pepper if needed, then divide into bowls, sprinkle with cilantro and serve!