Preheat the oven to 500°F and place the rack in the center position. Line a large baking sheet pan with aluminum foil to make cleanup easier (optional).
Meanwhile, wash, dry, and trim ends of each squash; halve squash lengthwise and scrape out the seeds from each half.
2 medium spaghetti squash
Rub the inside of the squash with oil and season with salt and pepper. Arrange the squash halves cut-side-down on the baking sheet.
4 tsp extra virgin olive oil
1 tsp salt
½ tsp black pepper
Place squash halves in the oven (it doesn't have to be fully heated) and roast until tender, so a knife can easily pierce through the flesh, about 30 minutes.
Meanwhile, wash, dry, and cut the cauliflower heads into quarters, then trim off and discard the leaves and thick stem. Cut into bite-sized pieces. Transfer to a large pot, season with salt, and cover with hot water (from the tap).
2 medium heads cauliflower
1 tsp salt
Place pot with the cauliflower over high heat, cover, and bring to a boil. Reduce to a simmer and cook until fork-tender, 4-6 minutes.
While the cauliflower cooks, peel and roughly chop garlic; transfer to a small bowl.
4 cloves garlic
Add milk, nutritional yeast, oil, salt, and pepper to the bowl with the garlic; stir to combine and set aside for the sauce.
8 fl oz (1 cup) whole milk
¼ cup nutritional yeast flakes
2 tsp extra virgin olive oil
½ tsp salt
¼ tsp black pepper
Finely grate Parmesan and set aside.
2 oz Parmesan cheese
Place peas in a colander. When the cauliflower is done, pour over the peas into the colander to drain.
2 cups frozen peas
Transfer half the cauliflower to a medium bowl and reserve for the sauce. Return remaining cauliflower and peas to the pot, cover, and set aside to keep warm.
Working in batches to best fit your blender, combine reserved cauliflower and garlic-milk mixture in a blender and blend on high until smooth. Add water, 1 tablespoon at a time, if necessary, to reach a sauce-like consistency.
Remove squash from the oven and allow to cool slightly, about 5 minutes. Scrape the inside of the squash with a fork to separate into spaghetti-like strands. (Use an oven mitt or towel to hold it with your other hand.)
To serve, divide squash between plates. Top with sauce, remaining cauliflower, peas, Parmesan, and pumpkin seeds. Enjoy!