Cook the linguine according to package directions in a large pot of salted water. Drain and set aside, reserving 1/2 cup pasta water in case you need to thin the sauce later.

In a large skillet over medium-high heat, brown the ground beef for 5-7 minutes, breaking it up with a wooden spoon. The beef should develop a nice caramelized color for maximum flavor. Drain excess fat if needed.

Add minced garlic to the beef and cook for 1 minute until fragrant. Don't let the garlic burn or it will taste bitter.

Pour in soy sauce, beef broth, brown sugar, hoisin sauce, ginger, black pepper, and red pepper flakes. Stir well and let the mixture simmer for 2-3 minutes.

In a small bowl, whisk cornstarch with cold water until completely smooth. Slowly pour this mixture into the skillet while stirring constantly to prevent lumps. The sauce should thicken within 1-2 minutes.

Add the cooked linguine to the skillet and toss everything together for 2-3 minutes until the noodles are completely coated with the glossy sauce. If the sauce seems too thick, add a splash of the reserved pasta water.

Remove from heat and garnish with sliced green onions before serving immediately.