Warm the olive oil in a large skillet over medium-high heat. Add the chopped onion and jalapeno, if using, to the warm oil and cook for 4-5 minutes, just until it begins to soften. Stir in the garlic, salt, cumin, chipotle powder, and cayenne and cook just until fragrant, about 30 seconds.
Stir in the beans, followed quickly by the broth. Bring to a boil, then reduce heat to medium and simmer until the beans are tender and most of the liquid has evaporated, 8-10 minutes. Remove from heat, stir in the lime juice and chopped cilantro, and adjust seasonings to taste.
Assemble tacos as desired and serve.
Notes
If you have any leftover bean mixture, it makes terrific quesadillas, and is also yummy mixed into scrambled eggs for a protein-rich breakfast or lunch!