Preheat the oven to 400 degrees and spray a 9x9 pan with cooking oil. Set aside.
Into the pitcher of a high speed blender, add the cashews, water, pumpkin, nutritional yeast and salt. Blend until creamy and smooth.
Add the oil to a medium skillet over medium-high heat. Add in the onion and cook until translucent, about 5-7 minutes. Add in the garlic and sauté for another 30 seconds. Add in the blended mixture and stir to combine.
Add in the potatoes and toss to coat. Transfer the mixture to the baking dish and top with vegan parm. Bake for 40-50 minutes or until the top is golden brown and the potatoes are cooked through. Serve.