Roast the poblanos and jalapeno in a dry skillet, directly over a gas flame or under the broiler, turning often, until charred all over. Transfer the poblanos to a bowl, cover with plastic wrap and let cool for 5 minutes.
Rub the blackened skin off of the peppers and remove the ribs and seeds of the peppers.
In a large soup pot, heat 1 tbsp of oil over medium high heat. Add the ground beef and cook, crumbling it with a spoon, until browned. Add the onions and cook until softened, about 5 minutes. Add the minced garlic and ground cumin and let cook for about thirty more seconds.
Add the black beans and beef stock. Bring to a boil, reduce heat and let simmer for 15-20 minutes. Add the fresh lime juice, and season with salt and pepper to taste. Serve topped with sour cream or cheddar cheese.