Pre-heat the oven to 450 degrees F. Line a baking sheet with aluminum foil or parchment paper and arrange the chops in a single layer on the baking sheet. Season the chops with salt and pepper. Arrange the slices of blood oranges and the rosemary sprigs alongside the lamb chops on the tray. Drizzle the olive oil on the lamb, oranges and the rosemary sprigs. Use your hands or toss to coat evenly. Let the lamb chops stand at room temperature for 20-30 minutes. Roast until the oranges are charred and an instant-read thermometer inserted in the thickest part of a chop registers 140 degrees F (medium-rare), about 12 to 15 minutes. Cut the orange slices and serve alongside the lamb or squeeze on the orange juice and serve.