In a small bowl, combine soy sauce, grated ginger, brown sugar, sesame oil, cayenne pepper, and minced garlic.

Pour the marinade into a large ziploc bag.

Add the sirloin steak to the bag, ensuring it is fully coated with the marinade.

Seal the bag and refrigerate for 1 to 4 hours, turning the bag occasionally to evenly distribute the marinade.

Preheat a ridged grill pan over medium-high heat until very hot.

Remove the steak from the bag, reserving the marinade.

Pat the steak dry with paper towels.

Grill the steak for 6 to 8 minutes per side for a medium-rare finish.

Remove the steak from the grill to a cutting board and let it rest for 10 minutes.

Pour the reserved marinade into a 1-quart saucepan.

Add 2 tablespoons of water to the marinade in the saucepan.

Bring the marinade to a boil over high heat and boil for 2 minutes.

Slice the steak thinly diagonally against the grain.

Serve the sliced steak with the cooked marinade.