Preheat oven to 100°C (approximately 350°F). Peel pumpkin, cut in half and scrape out the seeds and fibrous interior with a spoon (if Hokkaido variety, do not peel just wash and pat dry). Cut the flesh into 3 cm (approximately 1 inch) wide pieces. Peel garlic and chop coarsely. Rinse rosemary, pluck the needles and chop. Grease a baking sheet with olive oil and distribute the pumpkin slices on top. Season with salt, pepper, ginger and rosemary. Sprinkle garlic and remaining oil over the top. Bake in preheated oven.
Bake 30-40 minutes, until the pumpkin is soft.