Heat the oil in a large skillet over medium-high heat. Season the lamb with ½ teaspoon salt and ¼ teaspoon pepper.
Cook lamb to the desired doneness, 4 to 5 minutes per side for medium-rare. Transfer to plates.
Return the skillet to medium-high heat. Add the cauliflower and cook, tossing frequently, until golden, 1 to 2 minutes.
Add the raisins and ½ cup water and cook, covered, until the cauliflower is just tender and the water has evaporated, 2 to 3 minutes.
Stir in the scallions and capers. Serve with the lamb.