In a large pot, sauté the diced onion and minced garlic over medium heat until softened and fragrant, about 3-4 minutes.
Stir in the black beans, tomatoes, chipotle pepper, stock, oregano, salt, and black pepper. Bring the mixture to a simmer.
Reduce heat and let simmer for 15-20 minutes, allowing flavors to meld.
Using an immersion blender, blend part of the soup to thicken it slightly while leaving some beans whole for texture. (Alternatively, transfer half the soup to a blender, blend until smooth, and return to the pot.)
Taste and adjust seasoning if needed. Serve hot.