Prepare the sauce
Melt peanut butter and lard in a microwave-safe bowl (or over simmering water) until smooth, stirring as needed.
Whisk in garlic oil, dark soy sauce, and toasted sesame oil.
Cook the noodles
Boil a medium pot of water. Cook noodles until just shy of al dente, about 5 minutes; they should be cooked through and pleasantly chewy.
Reserve 1/4 cup noodle cooking water, then drain.
Toss and serve
Whisk 1 1/2 tablespoons noodle cooking water into the sauce (add more water 1 tablespoon at a time if the sauce is too thick).
Immediately toss noodles and scallions with the sauce. Serve right away.