In a large resealable plastic bag, whisk together the soy sauce, olive oil, honey, minced garlic, chopped rosemary, black pepper and kosher salt until combined.
Add the flank steak to the bag and turn it to coat thoroughly in the marinade; press out excess air and seal the bag.
Refrigerate the sealed bag for 2 to 10 hours, turning the bag occasionally to redistribute the marinade.
When ready to cook, drain and discard the marinade and let the steak sit at room temperature for about 15 minutes.
Preheat a grill to medium-high heat.
Grill the steak 4 to 6 minutes per side for medium-rare, or until it reaches your desired doneness.
Transfer the steak to a cutting board and let it rest for 5 minutes.
Slice the steak thinly against the grain into strips and serve.