Preheat oven to 220 degrees C. Cook the pumpkin in a large saucepan of boiling water until just tender. Drain and set aside.
Heat 2 tablespoons oil in a large non-stick frying pan or skillet over high heat. Add half the lamb and cook. Stir occasionally, until brown and just cooked through. Transfer to a plate and repeat with remaining lamb.
Add onion, sugar and 1 tablespoon oil to non-stick frying pan, cook until onion is soft, transparent and caramelised. Move to small plate.
Place the pizza base on a baking tray and spread with pizza sauce. Sprinkle with half the Mozzarella cheese. Spread pumpkin and onion evenly over pizza base. Top with lamb, haloumi and rosemary. Sprinkle with remaining Mozzarella.
Bake in preheated oven, for 12-15 minutes or until cheese melts and is light golden. Remove from oven.
Sprinkle with rocket and slice into 6 pieces. Enjoy!
A great shortcut is to make this with leftover lamb roast, remember to make extra roast pumpkin though!