Step 1 Preheat oven to 200°C. Bring a large saucepan of water to the boil. Add pumpkin to pan and cook for 10 minutes, or until very tender. Drain pumpkin in a large colander and set aside.
Step 2 Bring another large saucepan of water to the boil. Add macaroni and cook according to packet instructions until al dente; drain.
Step 3 Meanwhile, heat olive oil in a large deep saucepan set over medium–high heat. Add carrot and zucchini; cook, stirring, for 5 minutes, or until soft. Add flour and cook, stirring, for 1 minute. Add skim milk to pan in a gradual stream and cook, stirring, for 2 minutes, or until vegetable sauce boils and thickens.
Step 4 Add cooked pumpkin to vegie sauce in pan. Use the back of a spoon to squash pumpkin into sauce until almost smooth. Stir macaroni and half of the cheese into sauce; season with cracked black pepper. Transfer mixture to a 6-cup baking dish and sprinkle with remaining cheese; bake for 15–20 minutes, or until golden.
Step 5 Meanwhile, steam Brussels sprouts and broccolini on the stovetop or in the microwave for 4–5 minutes, or until tender.
Step 6 Serve mac ’n’ cheese with steamed green vegies.