In a small bowl, mix the chili powder, cumin, and 1/2 teaspoon each salt and pepper.
Place the potatoes in a large bowl and the pork in another large bowl. Sprinkle half the spice mixture over the potatoes and the remaining half over the pork.
In a 12-inch (30-cm) nonstick or well-seasoned cast iron skillet over medium-high heat, warm the oil until shimmering. Reduce the heat to medium, add the potatoes, and then cover and cook, stirring occasionally, until well browned and almost tender, 10 to 15 minutes.
Stir in the pork and garlic and then cover and cook, stirring occasionally, until the pork is lightly browned and cooked through, 6 to 10 minutes. It may be necessary to reduce the heat to medium-low to keep the garlic from browning.
Season the pork and potatoes with salt and pepper and divvy them up among the tortillas along with any desired garnishes.