Preheat your oven to 425 degrees F. Set an oven rack to the lowest position.
Line a large rimmed baking sheet with parchment paper.
Wash and dry the pumpkin.
Place it in the microwave and cook it for one minute on high, to soften.
Carefully, using a very sharp chef's knife and back-and-forth sawing motions, cut the pumpkin in half (slice a sliver from the stem side first if you don't want to cut through the stem).
Use a large metal spoon to remove the pulp and the seeds. If some stubborn pulp remains, cut it with kitchen scissors. (If desired, save the seeds to make roasted pumpkin seeds).
Continue cutting each pumpkin half, using the sharp knife and sawing motions, into four one-inch-thick moon-shapped slices, discarding the ends.
Using a vegetable peeler, peel the skin off, then cut each pumpkin slice into 1-inch cubes.
Place the pumpkin cubes in a large bowl. Add the oil and spices. Use a large spoon, or your hands, to evenly coast the pumpkin chunks.
Arrange the pumpkin cubes in a single layer on the prepared baking sheet.
Bake them until tender, about 30 minutes, tossing them half way through.
Serve immediately. Top with fresh rosemary.