Cook pumpkin in a saucepan of boiling water for 8-10 minutes or until tender. Drain, reserving 1/2 cup liquid.
While pumpkin is cooking, heat a non-stick pan over medium heat. Add onion and garlic, and cook for 3-4 minutes until softened. Add spinach and cook, stirring until wilted.
Place pumpkin, onion, garlic, spinach, 1/2 cup reserved liquid, parsley and lentils into a food processor and blend until smooth and creamy. Set aside.
Cook macaroni in a large saucepan of boiling water, following packet instructions, until just tender. Drain well and return to the saucepan.
While macaroni is cooking, add 1-cup milk to a separate saucepan and slowly heat over medium-low heat. Add plain flour and whisk until smooth. Gradually whisk in remaining milk, and continue to heat on low for 4-5 minutes or until thickened.
Remove saucepan from the heat and whisk in cheddar cheese and pepper, until cheese is melted.
Pour the pureed pumpkin and cheese sauce over the macaroni and stir until well coated. Serve immediately with chopped parsley.