Add the diced onion, minced garlic, drained black beans, drained corn, and diced tomatoes with green chilies to the slow cooker.
Pour in the vegetable broth, then stir in the chili powder, ground cumin, and salt until evenly combined.
Cover and cook on low for 6 hours or on high for 3 hours.
Taste and adjust salt if needed.
Ladle into bowls and top each serving with chopped cilantro and a squeeze of lime.