In a 400º oven, roast the spaghetti squash, cut side down, using a baking dish or sheet pan. Roast for about 30-40 minutes or until the flesh is tender through the skin to the touch, or can be pierced easily with a fork or skewer.
While the squash is roasting, prepare all your vegetables. Add all the ingredients except for the nutritional yeast, hempseed, and beans. Mix well, cover the pot and place in the oven on a separate rack from the squash.
Roast in the oven, also at 400º for about 30-45 minutes, or until everything is tender and cooked through like a hearty pasta topping. Feel free to give it a stir halfway through the roasting process.
When the squash is done and cool enough to handle, using the tines of a fork, gently scrape the flesh out of the skin. It will roll out and take on the appearance of spaghetti. You can season the squash with salt, pepper, lemon, and-or olive oil, or just enjoy it plain. The vegetables will provide plenty of flavor.
Remove the roasted vegetables from the oven, stir in the nutritional yeast, and the cannellini beans and hempseed (optional). Give it a final taste for salt and pepper and adjust if needed.
To serve, place some spaghetti squash on a plate or platter, and top with the roasted vegetables, the same way you would with pasta. Sprinkle chopped parsley, extra nutritional yeast and-or hempseed for more garnish, if you want.
For a non-vegan version, you can stir in or top this with a flavorful cheese like Parmesan, Manchego, or goat cheese.