01 - Heat the vegetable oil in a large skillet over medium heat until it shimmers.
02 - Add the finely chopped onion and sauté for 3-4 minutes, stirring occasionally, until translucent and softened.
03 - Stir in the minced garlic and chopped chiles. Cook for 2 minutes until fragrant, taking care not to brown the garlic.
04 - Add the diced tomatoes and cook, stirring frequently, for 5 minutes until they soften and release their juices, forming a light sauce.
05 - Add the cubed potatoes, ground cumin, salt, and black pepper. Stir thoroughly to coat all the potatoes evenly in the sauce.
06 - Pour in 3/4 cup of water, just enough to partially cover the potatoes. Bring to a simmer, then cover and cook for 15-20 minutes, stirring occasionally, until the potatoes are fork-tender and the sauce has thickened.
07 - Taste and adjust the seasoning with additional salt or pepper as needed. Garnish with fresh chopped cilantro if desired. Serve hot with warm tortillas or use as a taco filling.