In a slow cooker, combine the rinsed black beans, diced onion, bell pepper, minced garlic, vegetable broth, cumin, smoked paprika, chili powder, salt, black pepper, and bay leaf. Stir to combine.
Add the diced tomatoes (with their juice) to the slow cooker and mix well.
Cover and cook on low for 8 hours or on high for 4 hours, until the beans are tender.
Once cooked, remove the bay leaf and stir in the olive oil and lime juice.
For a creamier texture, use an immersion blender to blend a portion of the soup, or transfer a cup or two to a blender and blend until smooth, then return it to the slow cooker.
Serve hot, garnished with fresh cilantro and a dollop of sour cream or Greek yogurt if desired.