Place the pumpkin, cauliflower, onion, and cashews in a large pot. Fill it with enough water to cover the vegetables plus about two inches.
Bring the water to a boil over medium-high heat and then reduce the heat and allow to simmer for about 15 minutes, or until the vegetables are fork tender.
Drain the vegetables and save the water. Allow the vegetables to cool slightly and then place them in a high-speed blender or food processor along with the nutritional yeast, garlic, onion powder, and salt. Add 2 cups of the reserved cooking water and blend until smooth and creamy. Add a little more water if the mixture is too thick. Keep in mind that it will thicken when it’s heated.
Heat the oil in a large pan over medium-high heat. Add the chopped leek a pinch of salt, and cook until it begins to caramelize, about 10 minutes. Add the white wine to the pan and cook until it reduces slightly, about 2 or 3 minutes.
Add the peas and tempeh bacon and stir to combine. Then pour the blended sauce into the pan and cook until it begins to simmer. Add a little of the reserved cooking water if it becomes too thick.
Remove from the heat and toss with the cooked pasta. Season with salt and pepper to taste. Divide among 4 plates and top with the fresh sage. Serve hot.