Heat oil in large pot over medium-high heat. Add onion. Cook, stirring, for 3 minutes or until light golden. Add pumpkin and 2 tablespoons water. Cook, stirring, for a further 2 minutes.
Stir in pasta, milk, stock and ½ cup hot water and bring to a simmer. Reduce heat and simmer, uncovered, stirring occasionally, for 8 minutes.
Stir in zucchini. Simmer, stirring occasionally, for a further 2-3 minutes or until pasta and vegetables are tender and sauce is thick and creamy.
Remove from heat, gradually add cheese, stirring until melted between additions. Serve seasoned with freshly ground pepper.