Bring a medium pot of water to a boil. In a medium microwave-safe bowl, combine peanut butter and lard. Microwave on high power, stirring every 10 seconds, until melted and smooth, about 45 seconds. (Alternatively, nest a metal bowl over a pan of barely simmering water and heat, stirring occasionally, until mixture is melted and smooth, about 2 minutes.)
Add garlic oil, dark soy sauce, and toasted sesame oil to peanut butter mixture, whisking to combine.
Add noodles to pot of boiling water and cook until just shy of al dente, about 5 minutes; noodles should be cooked through and pleasantly chewy.
Reserve ¼ cup of noodle cooking water. Using a colander, drain noodles. Whisk 1 ½ tablespoons noodle cooking water into peanut butter mixture. (If sauce is too thick, add additional noodle cooking water, 1 tablespoon at a time, until sauce is loose enough to evenly coat noodles.) Immediately transfer noodles and scallions to the bowl with the sauce, tossing to evenly coat. Serve immediately.
