In a large pot, warm the olive oil over medium-low heat. Add the garlic and cook until fragrant, for about 1-2 minutes.
Add the cauliflower to the pot then stir to combine. Pour in the vegetable broth and bring to a boil. Reduce to a low boil, cover with a lid and cook for about 10 minutes, until cauliflower is tender enough to mash with a spoon. Remove from heat and set aside.
In the bowl of a blender (preferably a high speed blender) add the hemp seeds, lemon juice, salt & pepper, nutritional yeast, onion powder and tamari (if using). Transfer the cauliflower and the broth from the pot to the blender. Blend on high speed until smooth and creamy. Taste test to see if you prefer more salt or onion powder.
Transfer the sauce back to the pot and simmer over low heat. Serve with 1 large roasted spaghetti squash or 8 ounces whole grain fettuccine. If using pasta, add it cooked with two tablespoons reserved pasta water to the pot with the sauce. The starches in the pasta water will make it even creamier. Serve warm with fresh parsley and/or vegan parmesan cheese (see notes), and enjoy!