Preheat the oven to 400 degrees. Cut the squash in half, remove the seeds (with a spoon or ice cream scooper), and bake on a baking sheet for about 25-45 minutes until tender (you should be able to pierce through the flesh easily). Note that baking times may vary based on the size and thickness of your squash. If you over-bake, the strands of spaghetti squash will become mushy (potato-like) when you scrape them out, so be sure not to over-bake them.
Using a spoon, start to scoop out and separate the flesh of the spaghetti squash until all that remains is the outer shell. You'll notice that the flesh of the squash comes out in strands similar to spaghetti (hence the name "spaghetti squash").
To Prepare the Baked Spaghetti Squash Dish:
Preheat the oven to 375 degrees.
In a large sauce pan, heat the butter and olive oil on medium heat.
Add the onions and garlic and cook for a few minutes until fragrant.
Add the flour and whisk to combine. Reduce the heat to medium-low and cook for a few minutes, stirring the flour/butter mixture occasionally.
Slowly add the milk and whisk continuously on medium heat until the mixture becomes smooth and starts to simmer. Continue to simmer, stirring frequently, until the sauce thickens in consistency. Make sure the sauce is thicker than a standard bechamel sauce. As a guide, the sauce is thick enough right when the sauce just starts to clump (just prior to this moment). In other words, the sauce should not pour out in a uniform stream. (see notes below)
Remove from heat and stir in the shredded vegan cheese (mozzarella or cheddar). Combine until smooth (i.e. the cheese should melt into the sauce).
Season with salt and pepper.
Add 5 1/2 cups cooked spaghetti squash and spinach leaves and combine.
Transfer everything to a baking dish (such as a 9x13 glass tray) and sprinkle the top with grated vegan parmesan cheese.
Bake for 40-45 minutes until the dish is bubbly and the top is golden. Note that if you do not bake for long enough, the dish may be slightly runny because the water released from the spinach did not have enough time to boil off.
Remove from the oven and let it sit for 5-10 minutes to allow the dish to finish cooking. Sprinkle some fresh ground black pepper (optional) and serve immediately. Enjoy!
Notes
Because of the addition of fresh spinach, this dish could come out quite watery If the white sauce is not thick enough prior to adding the squash and spinach. The water gets released from the spinach and will start to evaporate as the dish bakes in the oven. So by making the white sauce thicker in nature, you are lowering the total amount of liquid that needs to evaporate from the dish while baking.Vegan Cheese:
parmesan - I use Violife or Follow Your Heart brand
cheddar or mozzarella - use Miyako cheddar block, or Daiya cutting board collection
Microwave Method To Cook Spaghetti Squash:Wash the spaghetti squash. Poke holes (using a knife or sharp skewer) all around and place on top of a kitchen towel in the microwave. Microwave for 7 minutes. Rotate the squash 180 degrees so it cooks evenly. Microwave again for another 6 minutes. Adjust microwave times as needed (The exact times may vary depending on how large the squash is and how powerful your microwave is. To check whether the spaghetti squash is cooked through, you should be able to pierce through to the middle fairly easily.). Let the squash cool down. Cut in half lengthwise, remove and discard the seeds, and scoop out and separate the flesh of the spaghetti squash with a spoon until all that remains is the outer shell. You'll notice that the flesh of the squash comes out in strands similar to spaghetti (hence the name "spaghetti squash"). Note that the flesh should scoop out easily with a spoon. If not, then the squash may not be cooked all the way through.