Pat the steaks dry and let them sit at room temperature for 20 minutes before cooking.
In a small bowl, combine the crushed fennel seeds, minced garlic, lemon zest, olive oil, salt, and pepper into a paste.
Rub the fennel paste evenly over both sides of the steaks and let them rest for 10 minutes.
Toss the fennel wedges with olive oil and salt.
Heat a grill or heavy skillet over high heat until it is visibly smoking.
Sear the steaks for 3 to 4 minutes per side for medium-rare, without moving them during each side.
In the same pan or on the grill alongside, cook the fennel wedges for 4 to 5 minutes per side until deeply caramelized and tender at the core.
Remove the steaks and let them rest for 5 to 8 minutes before slicing against the grain.
Toss the caramelized fennel with red wine vinegar and fresh fennel fronds.
Slice the beef and serve immediately over or alongside the fennel.