Heat the oil in a large heavy-bottomed pot over medium-high heat. Sauté the onion and garlic (and jalapeno if using) for 3 to 4 minutes until the onion is soft and the garlic is fragrant, stirring frequently. (Do not let the mixture brown).
Add the cumin, coriander, and cayenne and let cook for 1 minute, stirring constantly. Add the black beans, stirring to combine. Add about 3 cups of vegetable stock (enough to just cover the beans) and bring the mixture to a boil. Stir in 1/4 cup of the chopped cilantro and reduce heat to a simmer. Let simmer for 15 minutes or until thickened, stirring occasionally.
Stir in additional broth if you want a thinner consistency. Stir in the remaining 1/4 cup of chopped cilantro, the lime juice, and season with salt and pepper to taste.
Serve with a dollop of Greek yogurt and additional chopped cilantro.
