Spiralize zucchini on the medium setting and set aside.
Add the soy sauce, sesame oil, rice vinegar, chili paste, sherry, brown sugar, and garlic to a skillet over medium-high heat. Let it bubble for a minute or two.
Meanwhile, combine the cornstarch and 2 tbsp cold water.
Stir the cornstarch mixture into the skillet. It should thicken the sauce up really quickly.
Add the zucchini noodles, peanuts, and scallions to the pan. Cook for a few minutes, tossing continuously (I use tongs to do this). The zucchini will release some water. Don't overcook the zucchini or it will be very limp and watery.
Sprinkle sesame seeds on top if desired. Serve immediately.