Add the olive oil to a medium saucepan and place over medium heat. Add the onion and jalapeno and cook for 2-3 minutes until the onions are tender. Add the garlic and cook for 1 minute, stirring often.
Add the black beans, chicken stock, onion powder, salt, and pepper to the pot and stir to combine.
Bring to a boil, then reduce the heat to medium-low and simmer. Cook for about 25 minutes until the liquid has reduced and the beans are thickened but not dry. Periodically, mash the beans with a potato masher.
Check the seasoning and add salt and pepper to taste. Transfer to a serving bowl before serving warm. Garnish with jalapeno slices and chopped cilantro if desired.