Heat a pot over medium high eat and add oil. Once the oil is hot add the cumin seeds and let them splutter for about 30 seconds. Next add the diced serranos, stir quickly and then add the diced onions. Cook the onions until they're transluelcent (about 4-5 minutes).
Add the garlic, stir until just fragrant and then add the rinsed black beans along with the taco seasoning, cumin powder, and chili powder. Stir well to comine. If the seasonings begin to stick and the pot looks dry, add 2-3 tbsp of water (just enough to get the beans to be a little wet and to scrape up any of the spices from the bottom of the pot). Cook the black beans on low heat for about 5-6 minutes.
Turn off the heat , add the cilantro and then use a potato masher to mash the beans slightly (you dont want them into a puree). Set aside.