1-Heat oven to 400°F. In a large roasting pan, toss the tomatoes, garlic, thyme, oil, 3/4 tsp salt and 1/2 tsp pepper.
2-Using a vegetable peeler, remove strips of orange zest. Thinly slice the zest. Nestle the lamb in the tomatoes, pushing them to the sides of the pan as necessary. Season the lamb with the cumin, 2 tsp salt and 3/4 tsp pepper, then rub with the orange zest.
3-Roast the lamb to desired doneness, 130°F for medium-rare, 90 to 105 minutes. Transfer the lamb to a cutting board and let rest for at least 15 minutes before slicing. Serve with the tomatoes and garlic.