Here's a meal elegant enough for any special occasion -- but don't wait for one to try it. Yukon Golds are the best spuds to use because they hold their shape as they roast.
In a bowl, combine lemon zest and juice, garlic, and rosemary; whisk in 1/4 cup plus 2 tablespoons oil. Season lamb with salt and pepper. Place in a large resealable bag, and add marinade. Seal bag, pressing to remove as much air as possible. Turn bag several times to coat lamb in marinade. Let sit at room temperature 1 hour (or refrigerate overnight), flipping bag halfway through.
Preheat oven to 450 degrees F. (If lamb was marinated overnight, remove from refrigerator 1 hour before cooking.) Toss potatoes with remaining 2 tablespoons oil, and season with salt and pepper. Transfer to a roasting pan, and roast 20 minutes.
Remove lamb from marinade, and season with salt and pepper. Push potatoes to edges of pan, add marinade and lamb, and roast 15 minutes. Reduce oven temperature to 300 degrees F, and cook 40 minutes. Add asparagus, tossing to coat in pan juices, and cook until lamb is medium-rare (an instant-read thermometer should read 130 degrees F when inserted in thickest part of lamb), about 20 minutes more.
Tent lamb with foil, and let rest 20 minutes before carving and serving. If necessary to fully cook vegetables, return them to oven while meat is resting.