1 spaghetti squash mine was medium sized. Prick with knife and roast on 350 for about an hour ( I bumped mine up to 450 for about 20 minutes then back to 350 for another 20 because I was starving ;) )
You can either cut your Brussel sprouts in half and throw them on baking sheet with squash for about the last 30 minutes ( drizzle with olive oil) or sauté them with the onions (if sautéing cut in quarters)
Once squash is done cut in half discard seeds and scrape the noodle like flesh out. In pan with olive oil (or about 2 tbsp butter) sauté 1 vidala onion until soft (if sautéing sprouts do those now too) add 1 large clove garlic minced and about 5 baby portabella mushrooms sliced. ( you'll need to add those last since the garlic will burn and the mushrooms will get soggy). Toss the squash in with a pad of butter, salt and pepper add Parmesan cheese and serve, I'm not kidding it is to die for.
If the computer wasn't broken I'd upload a pic :(