In a skillet set over medium-high heat, cook the lamb in a drizzle of oil, breaking up the meat with a spoon and sprinkling with cumin and a big pinch of salt, until it’s cooked through and no longer pink.
Add the spinach or chard leaves and cook for another minute to wilt the greens.
Open the pita halves into pockets and stuff with the lamb mixture and sliced cheese.
Wipe the skillet out with a paper towel and set back on the stovetop.
Cook the pitas until they’re golden and crisp, and the cheese melts.