Place butternut squash, sweet onion, and garlic clove in a mixing bowl. Add olive oil, season with a pinch of salt and pepper, mix. Transfer onto a baking sheet lined with parchment paper, roast for 20 minutes.
In a blender, add butternut squash and onion mix, cashews, nutritional yeast, arrowroot powder, water, and salt. Blend until smooth.
Reduce oven to 350F.
Bring a medium pot of water to a boil with a pinch of salt. Add pasta and cook to desired firmness. Strain pasta, add to a large bowl and mix with the 'cheese' sauce until evenly coated.
Line a muffin tin with silicone cups. Scoop 1/2 cup of pasta and sauce into each cup and sprinkle with breadcrumbs and chopped scallion over top.