Cook the pasta according to package directions in salted boiling water until al dente. Drain and set aside, reserving 1/2 cup pasta water.
Brown the beef in a large skillet over medium-high heat for 6-8 minutes, breaking it apart as it cooks. Drain excess fat, leaving about 1 tablespoon.
Add garlic to the beef and cook for 30 seconds, stirring constantly until fragrant.
Mix in seasonings by adding brown sugar, soy sauce, hoisin sauce, beef broth, ginger, black pepper, and red pepper flakes. Stir and simmer for 2 minutes.
Thicken the sauce by whisking cornstarch with water in a small bowl, then stirring it into the skillet. Cook for 1 minute until sauce becomes glossy and thick.
Combine with noodles by adding cooked pasta to the skillet and tossing with tongs until evenly coated.
Garnish and serve immediately with sliced green onions and sesame seeds.
