I cooked my squash by halving it, removing the seeds, and roasting at 375°F for about an hour. You can also roast whole for about the same time or in a microwave for 15–20 minutes; in both cases, pierce it a few times with a knife first to avoid explosion. Or boil it whole for 20–30 minutes; but you'll need a pot bigger than my biggest…
½ medium spaghetti squash
2 tsp olive oil
½ medium onion, finely chopped
4 cloves garlic, finely chopped
1 28oz can chopped tomatoes
(1 tsp dried thyme)
(½ tsp dried rosemary)
salt and freshly ground black pepper
3 tbsp chopped fresh basil
¼ cup grated parmesan
Cook the squash.
Saute onions and garlic until translucent; add tomatoes, thyme, and rosemary, and season; being to a boil; simmer 10m. Remove from heat and stir in basil.
Remove seeds from squash and scrape out flesh with a fork in spaghetti-like strands. Mix with sauce, top with Parmesan.
(Omitting the thyme and rosemary seems to work out OK, too.)
(From the American Institute for Cancer Research’s The New American Plate Cookbook.)