Sour cream, queso fresco, avocado, and lime juice for garnish
Place beans in a pot of water about 4 inches above surface level. Soak overnight. The next day, drain and reserve 1 cup of liquid.
Heat oil in heavy large pot over medium-high heat. Sauté onions until golden brown, about 5-8 minutes. Add garlic, chili powder, cumin, and cayenne. Stir 1 minute. Add the chipotle peppers and crushed tomatoes. Add the soaked and drained black turtle beans. Bring chili to boil, stirring occasionally. Reduce heat to medium-low and simmer with a lid slightly ajar. If the chili gets too dry add the reserved bean liquid so it covers the beans.
You can place the pot in a 325' F oven, a slow cooker, or keep it on a simmer on the stove until the beans are cooked through, 1-2 hours. Season to taste with salt and pepper.
Stir in the mangos and chopped cilantro. Serve with a dollop of sour cream, chunks of avocado, crumbled queso fresco, and a squeeze of lime juice.