Step 1 Preheat oven to 180°C. Place pumpkin in a single layer on a large tray lined with baking paper. Spray with oil and sprinkle with rosemary. Roast for 25–30 minutes, until tender and golden. Once cooked, roughly mash and set aside.
Step 2 Lightly spray an 8 cup-capacity lasagne dish with oil. In a bowl, combine ricotta, chives, egg and milk and mix until smooth.
Step 3 To assemble, spoon 1/4 cup of ricotta mixture over base of lasagne dish. Top with 1 lasagne sheet, cutting to fit if necessary. Top with half the pumpkin, a third of remaining ricotta mixture and half of the spinach. Repeat with another lasagne sheet, remaining pumpkin, a third of ricotta mixture and remaining spinach. Top with last lasagne sheet, and spread evenly with remaining ricotta mixture. Place tomatoes, cut side up, over ricotta. Sprinkle with mozzarella and bake for 30 minutes, until golden and bubbling. Stand for 5 minutes before garnishing with basil.