Heat 1 tablespoon olive oil in a large (12-inch) skillet over medium-high heat. Add the ground beef, season with a pinch of salt and pepper, and cook, breaking it up with a spoon, until browned and no longer pink and the internal temperature reaches 160°F (71°C), about 5-6 minutes. Transfer to a plate using a slotted spoon, leaving any fat in the pan.

Reduce heat to medium. Add the remaining 1 tablespoon olive oil to the skillet. Stir in the diced onion and cook until softened and translucent, about 4 minutes. Add the minced garlic and cook until fragrant, 30 seconds.

Sprinkle the cumin, smoked paprika, chili powder, and oregano over the onion mixture. Stir constantly for 1 minute to toast the spices and unlock their aroma.

Return the browned beef to the skillet. Add the diced potatoes and pour in the tomato sauce plus 1/2 cup water. Stir to combine. Bring the mixture to a gentle simmer, then cover the skillet with a lid.

Reduce heat to medium-low and cook, covered, for 15-20 minutes, stirring once halfway through, until the potatoes are fork-tender and the sauce has thickened slightly. If the mixture looks dry, add a splash more water.

Taste and adjust seasoning with salt and pepper. Remove from heat. Scatter chopped cilantro over the top and serve directly from the skillet with dollops of sour cream on the side, if using.