Preheat oven to 220C. Put the pumpkin and peeled shallots into a roasting dish and drizzle with ½ tablespoon olive oil. Roast for 20 minutes.
Brush the lamb rumps with the remaining oil and season with cracked white pepper. Heat a large non stick frypan over medium high heat and brown the outside of the lamb rumps. Place into a baking tray and add to the oven. Roast for 15 minutes for medium, 20 minutes for well done.
Whilst the vegetables and lamb are cooking, Heat a little of the thick coconut cream from the top of the can with the curry paste and cook over a medium heat until the oil start to separate from the curry paste. Add the remaining coconut milk, fish sauce and sugar and cook over a high heat until the sauce reduces by a third and thickens slightly.
Remove the lamb rump from the oven, cover and allow to rest for 10 minutes before slicing. Add the cherry tomatoes to the roasting tray and cook in the oven for 10 minutes or until the skins start to shrink.
To serve. Arrange the lettuce leaves on 4 serving plates, top with the roasted pumpkin, sliced lamb, shallots and tomatoes. Drizzle with the curry sauce. Accompany with steamed Jasmine rice.