Press beef into a broad even layer in a deep 12-inch saute pan over medium-high heat and cook undisturbed for 3 minutes. Turn in sections, break into small crumbles and cook for 4 to 5 minutes more until the beef reaches 160°F; drain excess fat.
Lower heat to medium, add sliced garlic and cook for 1 minute until softened but not dark. Add broth, salt, black pepper and crushed red pepper.
Bring to a simmer and add broken linguine in a loose layer. Cook uncovered over medium-low heat for 10 to 13 minutes, lifting and separating strands with tongs every 1 to 2 minutes; add reserved water if the pan dries before pasta is tender.
Leave a shallow layer of starchy broth in the pan, then remove from heat and toss in butter a piece at a time until the liquid lightly coats the strands.
Toss in lemon juice and zest and serve immediately without reducing the butter coating further.