01 - Heat vegetable oil in a large skillet over medium heat until shimmering.
02 - Add the chopped onion and sauté for 3 to 4 minutes, stirring occasionally, until translucent and softened.
03 - Stir in the minced garlic and chopped chiles. Cook for 2 minutes until fragrant and the chiles begin to soften.
04 - Add the diced tomatoes and cook, stirring frequently, for about 5 minutes until they break down and release their juices, forming a rustic sauce base.
05 - Add the cubed potatoes, ground cumin, salt, and black pepper. Stir thoroughly to coat all the potatoes evenly in the chile-tomato sauce.
06 - Pour in 3/4 cup water, just enough to partially submerge the potatoes. Bring to a simmer, then cover the skillet with a lid.
07 - Reduce heat to medium-low and cook covered for 15 to 20 minutes, stirring occasionally, until the potatoes are fork-tender and the sauce has thickened and clings to the potatoes.
08 - Taste and adjust salt and pepper as needed. Garnish with fresh chopped cilantro if desired. Serve hot with warm tortillas or use as a taco filling.