Heat oil in heavy pot over medium-high heat. Add onion, garlic, bell pepper and cilantro stems; sauté until onions are translucent. Add ground beef to pot, cook until beef is cooked through. Mix in chipotle chili powder, cumin, oregano and serrano peppers. Add beans, tomatoes with juice, broth, lime juice, zest and bay leaf. Bring soup to boil, reduce heat to medium, cover and cook for 15 minutes. Smash some of the beans in the pot with the back of a spoon and mix well. Simmer until the soup thickens, this will take about 15 minutes. Season to taste with salt and pepper.
Ladle soup into bowls. Top with lime crema, cilantro and chicharrones.