Heat a large pot of water for noodles. When water boils, salt it and add pasta to cook to al dente or with a bite to it.
While pasta cooks, heat a large, deep skillet over medium heat with 2 tablespoons vegetable or peanut oil. Add garlic, ginger, red bell pepper, and pepper flakes to the pan and cook together a couple of minutes, then add peanut butter and melt it. Whisk soy into peanut butter, then stir in pumpkin and curry paste. The sauce will be very thick. Turn down the heat to low. Add a ladle or 2 of pasta cooking water to thin sauce a bit and simmer over low heat. Adjust salt, to taste.
Heat a small to medium skillet over high heat. Pour the five-spice powder onto a plate with some salt. Press both sides of the shrimp and scallops into the powder. Add 3 tablespoons of remaining oil to hot skillet. Place the shrimp in the pan and cook 1 minute, flip and sear the other side until just opaque. Remove shrimp to a plate and set aside. Add another 3 tablespoons of oil to the skillet and heat back up to smoking. Add the scallops and sear on both sides until opaque. Remove scallops and add to the plate of shrimp.
Drain pasta and return pasta to the pot. Add the curry-pumpkin sauce and toss thoroughly. Serve noodles on 4 plated and top with scallions and seafood.