1) Preheat oven to 350 degrees. With a large chef knife, find the exact center of the spaghetti squash and stab through it. Press gently and the knife should slide through until it hits the cutting board.
2) Slice it! Now just press down gently on the knife to slice the squash in half. Do the same thing going the other direction.
3) Get a large spoon and scrape out all the guts and seeds from each half of the gourd.
4) Turn each half face down in a large baking dish and stab the skin a few times with a fork.
5) Bake these guys will need to bake at 350 for 60-75 minutes.
6) For sauce, about 10 minutes before the squash is done, add olive oil to a sauté pan over medium-high heat.
7) Once the oil is hot, add onions and cook for a minute or two until they are translucent.
8) Add mushrooms and cook for another 4-5 minutes until they are soft and have released their moisture.
9) Add the cream and turn down the heat to low.
10) Simmer for 5-10 minutes until the sauce has thickened a bit.
11) Add spinach in two batches. It should wilt really quickly.
12) Taste for salt and pepper and stir in the Dijon.
13) Remove the spaghetti squash from the oven and cool for a few minutes before moving on.
14) Using a fork, gently scrape at the flesh of the squash. Serve the sauce right over the spaghetti squash, just like pasta!