Whisk together the soy sauce, brown sugar, sesame oil, and sriracha in a small bowl until the sugar dissolves. Set aside. If you need to cook rice, start it now.

Brown the beef in a large skillet over medium-high heat, breaking it up, until no pink remains, about 5 minutes. Drain off most of the fat, leaving about 1 tablespoon in the pan.

Push beef to the side, add the garlic and ginger, and cook for 30 seconds until fragrant. Stir into the beef, pour in the sauce, and cook for 2 to 3 minutes, stirring constantly, until reduced and sticky.

Serve the beef over warm rice, and top with cucumber, green onions, and sesame seeds.