Heat the olive oil in a large saucepan over medium heat.
Save a couple tablespoons of red onion, bell pepper and jalapeño / serrano in a separate bowl for garnish.
Add the rest of red onion, red bell pepper and jalapeño / serrano to the pan and sauté until the onion is softened, about 2 minutes.
Add the garlic and continue cooking 2 minutes longer, stirring often.
Sprinkle the mixture with the cumin, coriander and oregano. Add a few grinds of black pepper and combine well. Continue cooking until the spices are fragrant, about 1 minutes, then stir in the chicken broth and black beans.
Cover and simmer for 30 minutes.
Turn off the heat and let cool for a few minutes. Purée with a hand-held immersion blender or conventional blender (if using a conventional blender, you will need to work in several batches).
Taste and adjust the seasoning as needed. To serve, ladle soup into serving bowls and garnish with cilantro, green onion and reserved red onion and bell pepper mix.