Bring a large pot of salted water to a boil. Add 10 ounces dried noodles and cook for 1 minute less than the package directions. Drain the noodles and rinse well under cool water.

Meanwhile, stir 1 pound lean ground beef and 3 tablespoons cornstarch together in a medium bowl until the cornstarch is evenly distributed.

Heat 1 tablespoon neutral oil in a large skillet over medium-high heat until shimmering. Add the ground beef and cook, breaking up the meat into medium pieces, until deeply browned, crispy in spots, and cooked through, 7 to 12 minutes.

Stir in 2 of the grated garlic cloves, 2 tablespoons of the soy sauce, 2 tablespoons of the water, and 1 tablespoon of the granulated sugar. Immediately remove the skillet from the heat. Stir and scrape up any browned bits from the bottom of the pan. Taste and season with more soy sauce as needed.

Whisk ¼ cup smooth peanut butter, 2 tablespoons rice vinegar, the remaining 2 tablespoons water, 2 tablespoons soy sauce, 2 to 3 tablespoons chili-garlic sauce, 1 tablespoon granulated sugar, 1 tablespoon toasted sesame oil, 2 teaspoons miso paste, and 1 grated garlic clove together in a large bowl. Whisk in more water 1 tablespoon at a time as needed to loosen to a pourable consistency. Add the noodles and toss to coat.

Divide the noodles between individual bowls. Top with the crispy beef, 2 matchstick-cut Persian cucumbers, 4 thinly sliced medium scallions, ¼ cup crushed roasted salted peanuts, and more chili-garlic sauce as desired.