Reduce the heat to medium and add onion, bell pepper, green beans and garlic. Cook, stirring, until beginning to soften, 5 to 7 minutes. Stir in chili powder and cumin and cook, stirring, until fragrant, about 30 seconds. Stir in broth, beans, tomatoes and the chopped poblanos; bring to a boil. Reduce heat to maintain a simmer and cook, stirring occasionally, until the vegetables are tender, about 15 minutes.