Add all of the glazed shiitake ingredients into a bowl and stir to combine. Let sit for 30 minutes to 1 hour to marinate.
Once the mushrooms are marinated, heat 2 teaspoons of oil over medium-high heat. Drain the shiitake mushrooms and add them to the hot pan. Cook, stirring frequently until the shiitakes are golden brown and have crispy edges. Remove the mushrooms from the pan and set aside.
Add the cashews to a high-speed blender along with the water, pumpkin, salt, pepper, and nutmeg. Blend until smooth. Set aside.
Add another 2 teaspoons of oil to the skillet. Add in the onion and cook until it is translucent, about 7-10 minutes. Add in the garlic and sauté for another 30 seconds. Add in the blended mixture along with the kale. Cover and cook until the kale is warmed through and wilted.
Bring a large pot of water to a boil. Add in a big pinch of salt and the pasta. Cook according to the package directions. Add the cooked pasta into the sauce, saving a few cups of the pasta water to thin out the sauce if needed. Add in the shiitake mushrooms and toss the pasta with the sauce to coat. If the sauce seems too thick, add in the reserved pasta water one-quarter cup at a time until desired consistency is reached.