In a large cast iron skillet (10 to 12 inch), heat vegetable oil over medium heat. Once the oil is shimmering, add potatoes, arranging them in a single layer cut-side down. Season with salt and pepper lightly.
Cover with a lid and cook without touching the potatoes until the bottoms are golden brown. This will take about 15 to 20 minutes.
While the potatoes are cooking, stir together cumin, chili powder, paprika, oregano, garlic powder, onion powder, cayenne and salt until combined. Set aside.
Uncover the skillet and flip each piece so the other cut side is down. Increase heat to medium-high heat and cook uncovered until golden brown on the bottom, about 5 to 10 minutes. Keep an eye on the potatoes to make sure they brown evenly.
Add butter, seasoning, and cilantro, stirring to combine. Cook, stirring occasionally, until the butter is melted, about 30 seconds to 1 minute.
Remove from heat. Taste and season with additional salt and pepper, if desired.
Place potatoes on a serving platter. Top with parmesan. Serve.