In a large soup pot, warm oil to medium heat. Add Onion and cook for 2-3 minutes. Add Bell pepper and cook for another 2 minutes. Add Garlic and 2 tomatoes, cook for 1-2 additional minutes. Season with salt & pepper.
Add Chipotle Pepper, oregano, chili powder, and cumin (Note my measurements on the spices are estimates, use as much of the flavors as you like).
Add 2 cans of the beans and the chicken stock. Bring to a boil. Reduce heat to a simmer. Simmer for about 15 minutes uncovered.
Using a hand-held blender, blend all ingredients while cooking in the pot. I like to make it fairly smooth, but some chunks are OK.
Taste for seasoning -- add additional if appropriate for your taste.
Add remaining beans and tomatoes. Simmer for another 10-20 minutes.
Add shrimp and cook for about 5-6 minutes, or until shrimp is pink and cooked through. Remove from heat. Add 1/2 cup fresh cilantro.
Serve in a bowl with remaining cilantro, avocado, scallions, and sour cream if desired.