Cook pasta according to al dente package directions less 1 minute. Reserve 1/2 cup pasta water. Drain pasta without rinsing.
In a large skillet over high heat, add olive oil and brown beef, breaking it up, about 2 minutes. Reduce to medium heat, season with salt and pepper, and stir in garlic, onions, chili flakes, Worcestershire sauce, tomato paste, parsley, and reserved pasta water. Simmer until meat is tender, about 8 to 10 minutes.
Toss in pasta and 1 cup mozzarella. Top with remaining cheese and cover with lid. Garnish with additional parsley.
Notes
For best results, do not rinse the pasta after cooking to keep the starch that helps the sauce adhere.