Drain the cashews and rinse them (cashews do not need to be soaked if using a quality high-speed blender).
Remove the pumpkin flesh from the skin (one side of the pumpkin should yield enough pumpkin, depending on the size of the pumpkin).
Add pumpkin, onions, garlic, shallot, cashews, nutritional yeast, salt, pepper, and vegetable broth to a high-speed blender; blend on high until smooth.
Blend the plant milk and flour, cornstarch, or arrowroot powder if making the nut-free version. Then add the remaining ingredients and blend again (skip the nuts and vegetable broth).
Set aside (If you make the sauce in advance, put it in the refrigerator and reheat it while the pasta cooks). If using immediately, leave it at room temperature.
Cook pasta according to package directions, reserving 1 cup of pasta water before draining.
If using frozen peas, cook with the pasta in the last 3 minutes.
Rinse pasta (with peas if using).
Return pasta to pan; pour in 1 cup of reserved pasta water, then sauce.
If adding kale, add it now. It will wilt immediately as it combines with hot pasta and reserved pasta water.
Stir to combine; add chopped sage.
Serve with small fresh sage and a sprinkle of red pepper flakes and Cashew Vegan Parmesan “Cheese."