Position a rack in the center of the oven and heat the oven to 425°F. Line a small roasting pan or rimmed baking sheet with foil (to make it easier to clean the glaze from the pan).
If necessary, trim the lamb so that only a thin layer of fat remains, being careful not to remove all the fat. Arrange the lamb bone side down in the roasting pan, interlocking the bone ends if necessary to make them fit. Season each rack generously with salt and pepper.
In a small bowl, combine the honey, vinegar, cumin, ancho chile powder, and a pinch each of salt and pepper. Brush the surface of the meat with about half (1/4 cup) of the glaze.
Roast, brushing the lamb after 10 minutes and then again every 5 minutes with the glaze that has begun to caramelize on the roasting pan, until an instant-read thermometer inserted close to but not touching the bones reads 125°F for rare or 130° to 135°F for medium rare, about 20 minutes for rare and 25 minutes for medium rare.
Meanwhile, pour the remaining glaze into a small saucepan, add the orange juice and garlic, and bring to a simmer over medium-high heat. Simmer until reduced to a slightly syrupy glaze, about 7 minutes. Add the herbs, if using.
Let the lamb rest for about 5 minutes. Cut between the bones to carve the racks into chops and drizzle each chop with a little of the glaze before serving.
Serve herb-flecked couscous or rice pilaf alongside.