To make crema, immerse raw cashews in room-temperature water and soak at least 1 hour. Drain and reserve.
Toast cumin in small, dry, heavy skillet over medium heat for about 1 minute, until fragrant. Transfer to spice grinder, let cool, and grind finely. In blender, combine cashews, cumin, lime juice, water, and salt. Start blender on lowest speed and gradually increase to highest speed. Blend at least 1 minute, until a creamy consistency. Pour into serving bowl and set aside.
To make pumpkin seeds, heat oil in heavy skillet over medium heat.
When oil is hot, add pumpkin seeds and sauté approximately 2 minutes, taking care that they do not burn. The seeds will begin to puff up and pop. Once they appear toasted, immediately pour them into bowl. Toss with cayenne and salt and set aside.
To make filling, heat oil in large, heavy skillet over medium heat. Add onion and sauté 3 minutes, until softened. Add garlic and sauté 1 minute more. Add squash and sauté 6 to 7 minutes, until squash begins to soften. Season with chile powder and salt.
Add kale and cook, stirring, about 1 minute, until it begins to wilt. Remove from heat, taste, and adjust seasoning with salt if needed.
Serve with tortillas, crema, pumpkin seeds, onion, cilantro, and salsa. To assemble each taco, invite guests to spoon about ½ cup of warm filling into a tortilla and top with crema and pumpkin seeds. If guests prefer more toppings, they can finish with onion, cilantro, and salsa.